@Chrior:
Sorry if I sounded rude, but I really meant to use sarcasm as a way to make you look at your own argument from a different perspective. I could elaborate a wall of text about this issue but it seems Count Mario has done so already, as always. Shortly, I wanted to say that:
1. Sunny is a crewmate; not exactly like one of the Straw hats, but an essential friend who carries the crew throughout their journey. Having it be unceremoniously destroyed just like this and left behind is not what One Piece is about at all. The Straw Hats aren't about to sacrifice one of their own comrades to such a fate. Pedro was already enough of a sacrifice and he wasn't even a crew member (not to mention he didn't have long to live anyway; and the debate about him being truly dead isn't really over)!
2. Sunny was born as a successor to Merry, even inheriting its (literal) spirit! We have been through the story of losing the ship and all of the drama that comes with it. Would this situation be exactly the same? No, of course not. Merry was broken many many times and shoddily repaired by Usopp until it could no longer continue sailing. In a certain sense, Merry was a metaphor for Usopp himself and his position in the crew, a 'tool' for his character development. The Sunny, on the other hand, is Franky's masterpiece, intricately tied to his dream. Which leads to…
3. Sunny being destroyed is not an obstacle to Franky that must be surpassed to realize his dream. It is the destruction of his dream. He wanted to build a ship to surpass Oro Jackson, one that could carry the Pirate King around the world and which would be maintained by Franky as the shipwright. The Sunny was built with the best and rarest wood in the world, from Adam Tree; which was bought with the money the Franky Family stole from the Straw Hats, essentially meaning that the efforts of the crew in previous arcs (including Merry) rewarded them with the construction of the Thousand Sunny. Its destruction would mean a way way tougher blow than the loss of Merry. It would be a defeat even worse than Sabaody, in the sense that they can't recover that piece of their adventures in any way. Would it be a nice dramatic twist? Yes, it would. But this is not the type of story One Piece is. This is a series where our main cast sets out on a big adventure to make their lives' dreams come true (and where barely anyone dies in the present time).
My idea is that the ship is heavily damaged and not destroyed. Not only this is also really bad and a tough reversal of fortunes (how can the crew escape with a badly damaged ship?), it is also a hurdle in Franky's dream. Remember, he wants to maintain the ship as they sail. So far, he has done nothing of the sort, unlike Usopp back in the day. This is his chance to prove he still has his shipwright skills and to take another step towards his dream, by taking this chance to improve the Sunny. Not only that, someone in this thread posted the time we spent with the Going Merry and the time we have been with the Thousand Sunny. It turns out that the Sunny already surpassed Merry. A final makeover to make things fresh wouldn't hurt at all, I think. A new design for the final strech of the series. Sounds good to me. Not something radical, but something new.
--- Update From New Post Merge ---
That's... exactly the point. See post above. Usopp's character development is even directly tied to the ship. The point is, destroying the Sunny is making Franky realise that his dream can not come true. It makes as much sense as Usopp accepting that he is always going to be a weak coward and give up on his dream.
It's a remarkable post, but i disagree.
Oda won't let the weak factor of Usopp to go at the middle of the series, whatever the reason that might pop-up. He will remain coward and weak to our eyes, and only at the end, when the whole world acknowledges him to be brave is when he will let it go.
I can understand the link with Usopp and the Sunny, but not share it like it was with Merry. Merry being Kaya's gift is a huge drive for Usopp to cherish it, both coming from Syrup village makes me understand that there is deeper connection with it more like with any other Strawhat, Sunny can perfectly have Merry's Klabauterrman, but the roots of Merry are irreplaceable to my eyes, specially when Usopp doesn't even has to worry about it, because is Franky's dream to make it functional.
Finally, Usopp has already showed that can do things that no one else can do, has already showed an endurance compared to Luffy who's owner of a rubber body, and got the enough wit to face any kind of hardship like the bravest warrior… he already, by himself, achieved his dream.
I agree on your Sunny comment, i also think it's only damaged, mostly because:
He already made the last one.
@Strooger:
That's stretching it quite a bit.
MC's character development only has two pillars standing high compared to the others, Usopp and Zoro.
Usopp's good and Zoro's fine.
Usopp's one is good because he doesn't has a great fate to fulfill, but remarkable enough because he fights more or less with Oda himself, it's a thing that goes with how Oda portrays him as a courageous or as a warrior. He plays with those two factors from time to time, and as how Usopp's dream is "to become a brave warrior of the sea", he pretty much has to have the credits to say to others that he has tested all "what the sea has" to trying to overcome him.
Reality and most important is that he already has proved to be brave and formidable warrior, you can say that he already catched his dream and bring facts to argue about it, so only the author is the responsible for the notion of what has happened and what he has learned about it.
Zoro is pretty much the same behaviour since his introduction, he got a nice development to my eyes for putting his friends and his own perception of pirate above/forward to the one of becoming world's best swordman, he's no longer proud when it comes to what he protects, as his master taught him that way, it's nice to see it… like what a real shonen MC should behave. That contrast is nice to see to me.
Nami is a comedy resource since Arabasta, do i have seen her drawing a map?? She's now focused to be strong enough to do something... like Usopp's worries at W7, but without saying it, she doesn't excels at all, to me.
Robin is the translator - comedy resource atm, her full review at Enies Lobby was nice 400 chapter ago, trusting like she never did before is a development to some readers, to me isn't... i feel when i see her to be more like a furniture many times... she awakes when there is a Poneglyph.
Chopper is the cuteness factor, a cure to all?? To the same corner where Nami is, he's thinking the same as Usopp in this arc.
Franky is already an adult, he was amazing back there and showed almost anything that might be of use to the story, now i feel him to be more manly than ever and lost some attributes that showed before, he only has to supervise his dream to be fulfilled. Hope this chapter proves him to show more of his feelings that are missed to me.
Brook is the best of this trash-can, i can still feel his regards and respect to Luffy for let him joining just like that first time, he is a good character plus a good comedy resource, development? He got a little, he knows that Luffy will become Pirate King, puts his life on the line for it, like the ones that really have good development... but still don't put him above this, because he cares more for others than for him, to me, meeting Laboon is a weak dream enough to cruise the Grand Line.
Sanji is the worst, got character development... he learned to a new sweet recipe, All Blue? Still Kicking? Okama kempo?? No, yes, no. The development of the series helped us to notice how mediocre is he, he "un-developed", now he doesn't get fights and Jinbe's crew status is shattering his title as Monster Trio member.
Luffy, he's pretty much the same, more stupid tho. He won't change ever, i can expect nothing from him, he will always defeat the strongest guy, because nobody else can do it, half of Japan likes it, many readers love it, i despise it. 
What was the point of Ace's death? Him, getting stronger xD What a waste.
My reflexion point about this character development is what all of this MC are, and that is pirates.
One Piece's pirates go and fight to fulfill their dreams, and it's a world where pirates have the upper-hand to do so, therefore you can expect them to dream big and high... there are some characters that for story's fault, this doesn't shows as good as it sounds. Because we care for story more than characters, Oda's big point at storytelling is that he's the one who created a jigsaw-puzzle and drops pieces from time to time... so his characters aren't pretty much with a space to grow, so they remain as they were introduced first, and with so many character as this series has, it's normal from some to screw hard at their screen-time.
So when some of them, appear to be big or low, and whatever the reason, climb to catch their dreams again, is grateful to see that sight... and when you have MC that are always big, those are fated to fail on that department of "being pirates".
Nothing exists; even if something exists, nothing can be known about it. Even if something can be known about it,
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