[JAS84]

According to the entry on Wikipedia there are only five Sky Showcase exclusives - Simpsons and four Dreamwork Animation productions, only two of which are in active production, the other two have ended (one back in 2017, though that was apparently a Netflix production, and the others are Hulu/Peacock productions).

That being said, Simpsons is an international global success (quality of later series not withstanding), and it would be very unusual if it didn't continue in external syndication outside of Disney+.  When the show does end (as nothing lasts forever) and stops being syndicated and shown, Disney+ or whatever it calls itself by that point will probably be its final destination.

Oh, I expect Channel 4 to keep it. They get it a few years after Sky and Disney+. It's the first run rights that are likely to lapse, not the syndication/repeat rights.