2 complete different characters that have nothing in common.
Might as well say Sengoku and Garp will be alive when One Piece ends since Oda doesn't like killing off characters.
Then why Arlong is alive? Why Enel is alive? Both of them have none of plot relevance at this point, because one is in prison, if I recall correctly, and the other is on the freaking moon.
Crocodile HAD no story relevance after Alabasta. We didn't saw him again until several years later, during Impel Down. You have no way of telling if Oda hasn't planned anything like that for Doffy, you know? He isn't going to die.