You know, the complants about people dying are annoying me, because people here seem to want death for any other reason then a change of pace. That doesn't seem like a very good reason to kill someone.
Now, if the FF died that way, what point would it serve? What, that the BC can kill people? We saw that at Ohara. It give Franky a reason to join the crew. Eh, there are many other reasons, let's just leave it at that. No, if the FF had died right there then…well, it would just be randomly killing off characters. A forced tragedy. That's not good storytelling either.
Take, Dragonball Z, and the fight vs. Nappa. There, death served a purpose. As each fighter gave their lives to defeat Nappa, it made him seem more unstopppable, and made the situation seem more and more hopeless. It also made Goku's appearance all the more like a miracle.
Meanwhile, if the FF died in Enies Lobby, it would just make Franky sad. And it's not even unrealistic for them to survive either ,since the giants took most of the damage (but, wow, Paulie sure has a lot of rope huh?)
Now, while people do cheat death in One Piece, that doesn't mean that a bunch of cheap deaths will make up for it. One Piece is rarely...no wait...is never a story about tragedy. It's about victory, and a death toll only subtracts from the victory. Although, it would help if Oda stopped injuring hte minor characters so badly...
As for those who want the Merry to die, don't worry. It's will most likely sink after saving the SHs, unless Franky figures out a way to build his dreamship out of the Merry.
And for those who think the Merry appearing here is BS...wait til the next chapter.