He does have to come out and give is big rallies to stir up hate and bigotry against wizards. I wonder how hard it would be for a 20th level Assassin to one shot him while he is on stage?
If he does that he's vulnerable to scrying (choose one of his simulacra or magens as your target - you'll see them listening intently to something, even if you cant see or hear whats doing the talking).
He basically stuck hiding in a room alone (or with other mind blanked creatures) playing solitaire and spamming mind blank repeatedly till he dies, and nervously looking over his shoulder for a Dragonborn Cleric to appear and smack him silly.
That's a fate worse than death really.
If we really want to speed things up, a
20th level Diviner (on a day where he rolled a ew '1s' for its foretellings) could simply abduct a minion (via
Scrying, and
Legend Lore, and then
Plane Shift) and then cast
Dominate Monster on the minion (ordering it to return to its master) forcing it into a save result of '1', followed by casting
Magic Jar and then
Plane Shifting it back to the Material plane near the Sorcerer Kings lair (holding both the Magic Jar, and the giant rubber mace shaped shaped like a phallus)
As soon as the Dominated minion gets within 100' of the cowering Sorcerer King, you posses the Sorcerer King from your Magic Jar, foretelling his saving throw result into a roll of 1.
Then you order your minion to beat yourself to death with the giant rubber mace shaped like a phallus.
Works the same I guess.