Nothing, you just can't catch him.
Chat with our AI personalities
NO it doesn't
No it will not come back because it's a legendary Pokemon and there's only one of themActually it does come back. You have to wait a week and he will be there again to battle you.ACTUALLY, THE POKEMON DOES NOT COMEBACK UNLESS YOU RESTART YOUR GAME.
it wil never come back...
Once you kill Tornadus, you have two chances. Since it is a legendary Pokemon, there is only one of its kind, and will appear after the first one.
Well technically, you can't KILL a Pokemon. You can just make it faint. When you make a legendary Pokemon faint, it will be gone until you start a new game.