I expect the conjuror will be leaving soon ... with the epic spell gone, he'll be taking an exit soon (although probably after V has managed to teleported to the next destination). My guess would be that going after Xykon to unleash the sorceror's epic spell ... but lacking the necromancer or conjuror will lead to that particular mission failing (with the necromancer's absense making the elimination of Xykon impossible, and losing the conjuror would eliminate the teleport option for escaping).