Eric (ugh), deciding that he's had quite enough of this s**t, steers a ship through a whirling vortex of doom and uses its bowsprit to freaking impale Ursula right through the gut.
Walt Disney Studios
For whatever reason, this causes lighting to strike her for an effective electro-stab combo. If they'd only stuck an explosive in her mouth, they would have covered the shark kills from all four Jaws movies.
Ursula screams in agony and falls back into the ocean, the saltwater and electricity searing through the massive open wound in her belly and charring her huge, exposed intestines (that last part is implied but not shown). The horror of this fresh in everyone's mind, the king gets his trident back and makes everyone happy and everything better, somehow. Is there no problem a large-scale impalement can't solve?