It will slow him down for long enough for them to escape at least
Personally I thought he was going to become an iceberg the size of a mountain, to the extent that he couldn't even break it with his high strength. Oh well this works
Edit: Though that would take many cold spells. However as to my limited knowledge of D&D Tarries can't breath underwater does that mean he will keep repetitively "dieing" and regenerating before he can do anything to free himself?