I remember in Kings Quest 6 you can meet a guy early on in the bookstore which becomes relevant (but not critical?) right at the end. I never knew how relevant though, as the time I played it through right to the end wasn't one of the times when he'd happened to be in the bookstore early on.

I guess that's not enough of a dead end to block progress.

Maybe it'd be enough just to know what happens in the castle if Prince Alexander had befriended him. Otherwise I guess I'll carry that unresolved thread around with me for another ~25 years.

Edit: went looking for spoilers and yeah, alternate ending which admittedly sounds better than the one I got