Well Kuai has been a robot, a revenant, and possessed by a knife - might as well see what it's like to become goo. He'd be willing to test out the portal on himself if they need to send people around. He may hate technology with a passion but he's actually decent at it so he could operate the portal himself and send people away after they determine it doesn't turn people inside out.

Assuming the plan works and the World Eater is dealt with, he'd want to go back to his world. Death in Mortal Kombat doesn't work like death anywhere else and his fellow Grandmaster just happens to be able to teleport around the Netherrealm where are the dead are.

So that's convenient.

If they fail he'll probably insist on dying in the fight somehow because that's how he do. Unless anyone wants to forcibly drag him away.