This was apparently the first soul forge of a living person with a just executed soul. While it may have been reasonable to assume that resurrecting Ygerna would have killed Damian, I don't see how that would have had to have been the case.
Ygerna was dead, but still linked to the world of the living by the soul forge. Presumably that would have given protection from the memory eaters. She was stuck in one of her own memories, so that could have helped, as well.
We don't know what became of Maxos (yet) but he entered the hall of echoes alive. There is no reason to assume his search for power didn't lead him to other realms, or that he was trying to return to Rivellon. It is implied Maxos got into some kind of trouble, but we don't know when or what the situation is/was.
What makes you think Patriarch was fooled? He stopped short of mentioning what happened to Maxos, when he obviously could have given a warning. Maybe he figures what happened was necessary, so a warning would have only made things worse; maybe he just didn't want to interfere more than a bare minimum.
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