Most creatures die when they are 'sucked into the void, gone, and utterly destroyed'. The tarrasque simply doesn't. The void is full of destroyed tarrasques who are somehow, in some metaphysical way, still alive.


It's no different from how a disintegrate spell that reduces a creature to 0 but not -10 HP doesn't kill it, but does reduce it to a mere trace of dust - which kills most creatures very shortly thereafter for lack of air/food/water/etc.