[fjtorres]

A couple of the bigger ongoing franchises (163X and Honorverse) have expanded by extending the focus to other characters and settings within the common framework and bringing in other authors.
It allows for a broader exploration of the franchise milieu or concepts without necessarily falling into the "yet another episode" fan service model.

Now, some concepts naturally lend themselves to the "variations on a theme" episode model (STAR TREK, police procedurals, legal and medical dramas) but other concepts and stories don't lend themselves to sequels and trying to graft followups to a one-and-done tends to leave a bad taste and often devalues the original or drives the audience away.

Some times it is best to leave well enough alone.