Eh, I'm not too worried. It's not like they have more Greater Dispel Magics prepared than I have uses of Mystic Shield, especially with that reminder about CL. I could make this cheaper... Or buy more of them.
Yeah, and even if they do have enough, you've got so many actions that him dispelling and you re-casting is a recipe for success.
I don't think there are any abilities that grant mind control, and even if there were my cohort could survive long enough for the Sarrukh to finish choking to death in space. Remember, his magic doesn't work on the solstice, so no air summoning for him. If his body is lost forever in space, then his god doesn't know where it is and can't personally resurrect him, which is what true resurrection requires. Divine knowledge of the death. For all the god knows, Pi'it'lith simply vanished.
...what? True resurrection only requires you to be able to clearly identify the person to be resurrected. And don't say Set won't know he's dead. He knows everything that happens within 10 miles of the guy; he watched your cohort kill him. And even if he's blind that day, what do you think he's going to think when he can't see him any more the next morning? "Gosh, my high priest has mysteriously vanished, but is undoubtedly still alive?" Oh, and that's assuming you somehow bind his soul so that it doesn't move on to the afterlife. You know, the one where he's going to appear at his god's side the moment he dies.
That would be the way to do it, I suppose. Bind his soul, then launch the gem containing it into deep space. Of course, you'd have a hard time getting him to fail the will save, with the crappy save DCs spells cast from items have, and there's the question of whether a soul bound in a gem still counts as a worshiper for the purposes of divine sight.