User blog comment:Shinhwalee/Guide to Power Leveling Heavy Cruiser (CA) in World 3-2A/@comment-26110809-20150427171327/@comment-26348726-20150427172224

Nono, morale has nothing to do with whether a ship can be sunk or not.

The only way for a ship to be able to sink is to enter a new node while on 大破 (taiha) damage.