Roll all your dice because another player can heal your wound/s before your turn starts.
No, he's talking about the turn that the survivor dies, is he going to have 3 dice or 4. The answer is 4 because you determine your number of dice before the survivor dies.
But then on the turn after that, he will only have 2 survivors left, so he will only have 3 dice.
You're correct, though, that he may be able to convince another player to heal his survivor, but that's not always possible.