I know I'm setting myself up for disappointment but I hope when Della eventually returns (because we know she will) the new focus of the drama would be her trying to be the new main parent of the triplets after being gone for so long but the more she tries to be in their lives the more she begins to drive a wedge between Donald and the kids.
Maybe they could have a fight where Donald tells her that and Della goes out of line and tells him he's not the kids father and should butt off. Scrooge being a cunt of course would side with Della.
Donald then begins to feel more and more alienated by his family until we get a nice episode where he takes the triplets and Webby to hang out and have an adventure the five of them. The episode could end with him telling the triplets he'll always love them and tells Webby even though they're not related he loves her too just like she was his own daughter.
The episodes then ends revealing he's tired of Scrooge and Della's bullying and leaves to hang loose with Panchito and Jose. Della being the clueless prick she is sad but doesn't understand why he's leaving and Scrooge being stubborn as he is just lets him.
He could stop showing up for a good while but calls the kids everyday, but initially only Huey and Webby talks to him but Dewey and Louie feel betrayed. The season arc would focus on Della and Scrooge realizing they were wrong about how they treat Donald.
The finale could end with Jose and Panchito offering Donald to go to Brazil with them and he has to choose between them or his family before ultimately choosing his family and getting the support he deserves.
None of this will ever happen and nothing resembling this is going to happen, but man, wouldn't it be great?