It's possible that there could be some shenanigans that lead the order to the fortress. If Xykon gets destroyed Redcloak could tell the order that Xykon made an astral fortress for his phylactery, omit the fact that he has the real one, and then try to destroy Xykon and everything else by executing plan B while the order is occupied. I doubt that something like that would happen and if it did some seriously weird stuff like using the planet in the rift as a backup world would have to end up occurring.

Yeah it's unlikely the fortress will come up but anything's possible.