Well, somehow I think SA has a lot to lose from this situation. First because Terran is far away, further away than Caerwyn is, so Astroist armies would have to travel more, stay in the field less, and stay out longer. Second because Terran, on defense, would have support from the 'moot, which would quite strengthen its position. Third, because it would make SA as a religion very badly seen in the Maroccidens, losing foothold in there, should it fight the 'moot.
Why SA? This is a secular dispute between Terran and Caerwyn's successor. Astrum is merely championing the rights of the realm that will soon replace Caerwyn.
SA doesn't have much presence in the Moot anyway. I think we have one temple in D'Hara and only one in Terran, since a certain Chief Magistrate had one of his vassals close down the other one we had back when he was Senator of Chesny. Not likely to help him in this situation, actually, if anyone recalls that fact.
Edit: I take it back, we have three in Terran! Count me surprised. Of course only one of those regions actually sports any followers, I assume because its the one Senator Labell currently rules. In general, the only following we have in Terran is wherever he happens to be ruling at any given time. At least that's historically been the case.
