There's a moral issue, and there's a legal issue. From a moral standpoint, when he married her (in the Catholic faith) he made a vow to be faithful to her as long as she lived. He has not done so. That is what I judge harshly, based on my religious beliefs (which he claims to share.)
From a legal standpoint, I think there should be some kind of mechanism to deal with situations of this kind. "Common-law divorce" perhaps. "Termination of spousal responsibility." Something, so that a person's legal guardian wouldn't be someone who wants to kill them.
OK, if you bring in the Catholic issue I totally agree with you - I'm not saying they should have their marriage annulled by the Church, just the legal side dissolved. Net effect - Michael cannot remarry in the Catholic Church. We sure agree there.