hypothetical future, potential finales
I think the idea of an "end" is interesting. So far, the series has managed to maintain continuity, and not do a reboot. And though Sidney wasn't in the last, she could still come back for a definitive "final" appearance. All these things tend to happen in horror franchises, so it could still happen here. It might not for quite a long time, since the nature of the franchise allows for a changeover of characters while continuing the same story.
But I ponder. Maybe at some point they will do all those things, and I wonder how that would look? Because even if they're still making Scream movies in 50 years, Neve Campbell won't be in those, AI possibilities aside. So at some point they might actually announce, "This is Neve Campbell's last appearance," or "Next entry will be a reboot," or "Next entry will pretend none of the sequels happened and be it's own new continuity."
I just wonder how that would effect the series.