Just wanted to share an idea that I personally thought was genius, and thoroughly enjoyed.

Our current campaign is a homebrew where we play a group of undead adventurers in the service of a "good" lich. With five players and a DM all with different schedules, we invariably have a week or so a month of down time. Our DM has begun taking these opportunities to run one-shots based in the same world which either tell a major NPCs backstory, like a vampiress and her vampire daughter, or tell another story set in an iconic game location, such as a tavern filled with mimics run by Kenku in disguise. These one-shots have been a really fun and creative way of not only filling the down weeks and giving the main story more depth, but also allowing some of the newer players to experiment with different classes and races, and even to welcome new players to the table who aren't able to commit to an every week campaign.

Of course, we record the sessions for those that can't make them, so they can share in the stories and fun as well.