Until it cycles every bit of "nutrition" that it possibly can out of its own innards and dies of a lack of nourishment...or just flat out dies from stress. They can die from fucking anything, but stress also makes them even more brittle.
Come to think of it, I can' think of something yukkuri /can't/ die from. They could kill themselves on air.
...actually, they convince themselves they're drowning from a /lack/ of air, so...yeah.