Well, she shows up again in Nephew. Even though that's undoubtedly several years down the road, I hope they can get Tilda again to play Jadis. It'll be a much richer role.
Come to think of it, there's no reason they couldn't overlap production a bit with one of the other ones - there's essentially no "person" overlap between Nephew and any of the others, so you wouldn't have to worry about actors. (That's true of Horse as well). Of course, the behind-the-scenes talent would be the scarce resource. I'd rather have them take their time and do it well!