Irene knows what is to come, but is keeping Raven from it, because it's the only way to keep Raven alive. Both of them would sacrifice themselves for the other. This Destiny/Mystique thing is quite blatantly being portrayed as a relationship now, especially in the bits where Irene gives the future Raven/Forge thing her blessing. (So, welcome to the chart, you two. I'm sorry it didn't work out better for you in the end.) Raven (we're told here that's a self-picked name, by the way, but any idea that it was a cover identity has been forgotten) ought to have seen this coming. Destiny's quite old at this point.1 One day she was going to die. And Destiny would inevitably win at the sacrificial game. There's no way she'd allow Mystique to beat her to it, and no way Mystique could prevent it.
Mystique doesn't quite see it that way, of course. She already blames Forge for the end of Fall of the Mutants, where she believes Rogue died, and considers this another black mark against him. I can see another long-running plot arc starting there.