If you die while fighting a boss, like Snarbolax, and the boss dies, too (Bombs, another player,etc.), you should be able to revive w/o charge.
I was fighting Royal Jelly a while ago, and I died, I had no revives that time. But later on, he died because of a bomb, and I was still dead. Because I was dead, I can't get the rewards and finish the level. As I said before, you should be able to revive when you're dead when a boss dies.
PLS. IMPLEMENT THIS ON THE GAME!!!
Ask party members to revive you next time. +1, tough...