They can live for a fair while.
We used to have a 'pet' frog in the garage - we even left it a little tray of water. I guess it could get under the door when it wanted to, so it could get into the garden and eat flys and stuff.
I used to check under the car before I moved it, to make sure Kermit wasn't hiding under one of the wheels. It would have probably lived longer had I not reversed over it one morning...
