Bro tell Oda not to do a death scene
This heavily implies that he was meant to break free from that eventually. We also got a lot of Aokiji not doing what he was told to do and pulling Garps left right and center during Ohara and EL. Also defecting to become a pirate, lol. Its perfectly fine that Saul survived.
Kuma is a matter of viewpoint. Some might say that when the brain or memories are gone that this person is effectively dead.
Its canon that souls exist in One Piece. Kumas memories were erased, but not his soul.
Is he still alive, is it still him? You decide.