I like a lot of these ideas especially for Daria,Jane and Quinn. I could also see Jane also teaching art in her own unique way.
I would question if Brittany and Kevin would still be together.Same for Mac and Jodie but if they did I like the outcomes presented.

Daria is executive producer of sick sad world.
Jane is a jaded artist who actually makes money off of her art.
Quinn went on to become a nurse. She grew out of the materialistic and vain persona. She is currently engaged to a heart surgeon.
Brittany and Kevin both live in a trailer. Kevin currently works at Pizza King making minimum wage. He is up for the management position. Brittany bitterly stays at home and raises their bratty kid.
Helen went from being a workaholic to an alcoholic when she was forced to retire.
Jake has been driving Helen insane.
Trent's band never accomplished fame. He still lives in a haze.
Jodie and Mack are happily married. Jodie is working at a successful law firm. Mack is a professor at a college.
Upchuck invented something and got married to Andrea. Andrea dresses normal now, but is still a gothic girl at heart.
Turns out Joey and Jeffy are gay and Jamie is oblivious.
Sandi is still bitchy. She is now a gold digger.
Tiffany became a fashion consultant for the stars.
Stacy is running for mayor.