nah Oda doesn't like to kill characters off, right down to fodders. Most the deaths are in flashbacks, before the current timeline, those don't count.There is popular misconception that people in One Piece don't die.
Here are few guys who are dead in OP:
Big Characters who are dead- Whitebeard, Ace, Gol D Roger
Marines who are dead-Bellamere, Jaguar D Saul
Villains who are most likely dead- Vergo, Monet, Shiki(if u count strong world canon)
Dead Characters who were related to MC - Zoro's GF, Ussop mum, Robins country, Brooks previous crew, Franky's teacher etc.
Dead characters who were related to side MC- Laws family, Rebecca's mum, Shirhoshi mum etc...
Not counting fodders who died during Impel down Arc,Marineford Arc, Alabasta Arc, Dressrosa Arc.
That is One Piece's biggest downside is the handling of deaths. I'm fully expecting Vergo and Monet to be alive.
Also nice spoilers.