Short version:UXF team kills Apocalypse, triggering Archangel programming in Warren. Archangel declares himself Apocalypse's heir, and recruits Dark Beast, the Horsemen, and Genocide. Archangel commits genocide on a small Midwestern town killing thousands, and uses the site as a test for destroying then rebuilding the world. The UXF team assaults Archangel's citadel, and Betsy stabs Archangel in the chest with a "life seed" from the AoA dimension, killing him. The citadel collapses, and out of the rubble emerges Warren only he's "tabula rasa" -- a total blank slate, with no memory of who he was before. The Warren Worthington III that they knew is truly dead, and this "Angel" wears his face and body.
And that's not counting the whole "wings torn off by Morlocks, transformed into Archangel by Apocalypse" business that preceded it.
Huh, interesting. I know about the wings torn off/turned into Death stuff. I just haven't regularly read X books in like 20 years, sibce Fatal Attractions really. I've read some trades here and there but not a lot.