Yeah when you put it like that Mystique is following a pre-ordained path she has perhaps been told this was the only way by Irene herself.I mean I have no problem either way maybe Irene told her that only when Krakoa is down ,Irene will be resurrected as a result of the fallout, who knows? I just thought if the story allowed for Mystique to know the ultimate prophecy ,but through her own actions to test if Irene was right would enrich the story for example if she brought her back and then you have Xavier send Selene to kill Irene as a favour(with Selene having an axe to grind by being hoodwinked by Irene in Necrosha), I'd be like fine now Mystique's gotta do what she's gotta do