Reality Ensues; creators of works (famous and otherwise) are mortal, and subject to any number of cruel and unusual deaths, illnesses, family problems, etc.
Bob wants to move on and do something different.
Or he regards that work as something of an Old Shame.
Inverted: Bob was presumed dead after a ship-wreck. After his series got wrapped up once he made it back to civilization years later he restarted his series, retconning the end to Just A Dream. He includes a thanks to the well-meaning author who finished he series in the dedication.
Bob is diagnosed with cancer, and his prognosis is very poor. He immediately sets to work finding a way to finish Long Runner or have someone finish it for him.
Or he puts the series on hiatus, just in case he does survive.
Or he does die before finishing his work, but lives long enough to write a conclusion for an adaptation of the same work.
Bob survives months (or even years) of aggressive chemo and radiation therapy, surgery, etc. and has decided that continuing the work is no longer of importance to him, or that his energy levels are still too low to work effectively, or that there's no point in picking up where he left off.
Bob was hoping he'd pull through and be able to pick up where he left off, but he tragically did not survive.
Zig Zagged: ???
Averted: Bob is alive and well, and continuing his work on Long Runner.
Lampshaded: "This series could not be finished due to Bob's death."
Invoked: Bob is diagnosed with cancer, and his prognosis is very poor. Meanwhile, Long Runner is still the most popular show on TV.
Exploited: Bob was getting tired ofLong Runner anyway. The cancer diagnosis is an opportunity to intentionally make the series suck, in hopes that it will lose Ratings and get cancelled so he doesn't have to deal with it anymore.
Played For Drama: The son of the author continues a partially finished work. Grief stricken and feeling that he can't match his style he writes 'Unraveling as a semi-official conclusion. It is a dark tale about the collapse of reality after the death of god. Gaps in the story are left in, multiple considered outcomes are put back to back. The gaps and unresolved plot-holes receive an acknowledgement as characters are downright terrified at the implications. The whole thing ends in a Time Crash.