-My take has always been that if an effect is "cast" at the same event that brings the protection down then it is uninhibited by the protection. I even had a similar thought. [url]https://forum.atlas-games.com/t/no-mage-would-dare-right/4616/1]
-That being said a watching ward like spell would have problems. IMHO is that the hung spell is cast on the "target" then the effect is immediately suppressed. So the spell would have to overcome the "target's" MR when cast not the MR when it goes off. Not that there aren't a dozen ways to get around (or exploit) this.
-As far as how diligent Magi are about recasting Parma. That should entirely vary by saga and character. Though IMO most magi would be in the habit of waking up and recasting their parma at dawn. Less out of paranoid self protection and more out of habit. Meaning unless they have some sort of character trait or condition it would be unreasonable for another Magus or the SG to assume that they would be unprotected for more then a few minutes.
-Yeah ditto to what Gremlin said.
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-Casting a big Ritual like Aegis can't be timed out to the exact moment your previous spell expires in my opinion. I would imagine everyone would actually be out walking the perimeter of the covenant when it collapses. So I'm sure the ritual would not be finished.