jouleys:

WHAT IF the new campaign starts off with Matt telling the story of how Vox Machina became these established figures in Exandria, but one day they all mysteriously disappeared at the same time. Some of the most powerful people of the planet, just gone without a trace. And it stays a mystery for most of the campaign until the new party reaches a high enough level to find/rescue these legendary (but somewhat elderly) heroes. All while the players have no idea what happened to their old PCs.

Alternative ending: The new party finally finds VM drinking mimosas on the beach of a remote tropical island; they just wanted to retire without making a big fuzz.

They could turn this into a reverse Persephone thing! One day, the surviving member of VM just decided to spend half their year or so with Vax at the Raven Queen’s domain. Keep in mind half a year in-game is about twice the length of the Chroma Conclave arc.