What storylines were seemingly dropped but were then resolved years after the fact?

The other day there was a post about dropped storylines on TV shows, and there are many. But that got me thinking that there have been times when a storyline was seemingly dropped, but years later the writers surprised everyone by resolving the story after all.

For example, in Breaking Bad season 1 there was a plot involving Marie having kleptomania, which was seemingly dropped, until it came back in season 4 due to Marie's stress over her husband's condition.

Long-running franchises like Star Trek or Doctor Who are well-known for bringing back forgotten plot points from decades ago, since the people writing the show now were fans back in the day.

And of course, a common reason for a storyline to be dropped is because an actor left the show and thus their character had to leave, but then years later the actor comes back and thus their character also gets to come back and resolve their storylines.

So what are some notable examples of seemingly dropped plot points being resolved years later?