Story needs a tragic, thats for sure, but it doesnt mean like every villain or friend have to die. Oda just makes a one and whole OP fanbase cries their tears off, think about Ace and Whitebeard. Next one to die is probarly Shanks, so wait for the drama folks.
I've said earlier that its not always so hard to predict, who will die and survive. It's Oda, so we can't be sure, but let's face it:
-Ace didn't had any future in the story. He's dream was to protect Whitebeard whose age had to come to the end.
-Merry was too old and broken to carry SH's forward.
-Shanks is also one of the old pirates. He already had fight with BB earlier, who clearly is our last villain, so you can't predict him dying when they meet next time. Teach get's stronger everyone time. Its not suprise if the tries to increase his power by killing one of the other Yonkos. Luffy and Law are after Kaidou, Kid, Hawkins and Apoo after Big Mom, so its logical that BB is after Shanks. This "New age" will take over.
Bellamy "Last speech" with Doflamingo proved, that he could still have future ahead. He has strong will to get more powerfull. Message was: he is not just one stupid bully, who got beaten.
If you want more examples, let me know.