I have completed the game, Dalia has gotten her mothers locket, and apparently disappeared from the game. I lost stormheart, but got the Mythical Stormheart and I went to the Oak Tree and nothing happened? Am I going to have to start completely over?

Did you see if she's in Homestead?

Don't know if anything in here will help.

https://forums.crateentertainment.com/t/spoiler-solved-dalias-super-secret-quest/29450

Okay, the quest, and all the items can drop again, even if you already have it. You just play with someone who hasn't done the quests.