As it would be history if Ariel was a human Princess and Eric it was the son of the King of the sea. Obviously the history not be called the Little Mermaid.
Idea: Triton continues to deny Ariel her wish of being human, since her way of handling things on her own has shown that she is NOT ready to make her own decisions. But Eric doesn't want to give her up. THIS brings in Morgana (who is NOT a villain, but rather ends up being the Good Witch to Ursula's Wicked Witch) who gives Eric a potion to become a merman but this puts Eric into a state of indecision because if he becomes a merman to be with Ariel than his kingdom will be left without an heir...