While putting away some DVDs, I glanced at the animated "Lord of the Rings" from the 70s and remembered how they ran out of money and barely got halfway through the story and the movie ended. Of course you can read the book to see how it ended.
But that jogged my memory to Marvel's "Man From Atlantis" series based on the TV show where a pre-"Dallas" Patrick Duffy played an aquatic amnesiac, Mark Harris, who was trying to learn where he came from. The show was OK and the comic wasn't bad either. It had great Frank Robbins artwork, matching his "Invaders" and "Captain America". Anyway, #7 had Mark completing a mission successfully, returning to the sub where his research center allies were, only to find them acting like little children, apparently caused by some Mister Mxyzptlk wannabe. It was a standard 'to be continued' but it was the last issue!! And at the bottom of the final page, they said it was the last issue!
Nowadays, when a series is facing cancellation, the current creators usually have a chance to tie up any loose ends. My question is: Does anyone else have an example of a book cancelled in mid-adventure with no resolution published in another title, like "Marvel Team-Up" or "Brave and the Bold"?
Spectacular Spider-Man #17 depicted the break-up of the Champions after the events of the last issue of their own title, but I've not seen the latter and don't know to what extent readers had been left hanging.
The Wizard's attempt to destroy the Justice Society storyline from Secret Society of Super-Villains was wound up in Justice League of America ##166, via a flashback.