If your dragon dies it can be quite sad...and also frustrating. However, there is a way to get it back, if you have a graveyard.

You can purchase a Graveyard, then if a dragon dies it should appear in the graveyard, under most circumstances. You are then able to revive it using either 2 potions, or 3 cash. You can buy cash with real money to get the dragon back quickly, or try requesting potions of some of your friends.