The other fun thing about the crossover arc is that it seems that Magneto was literally seconds from following them back to the Ultimate Universe before realizing someone had to stay behind to wreck the portal. And that, in turn, means that you can picture the AU in which zombieverse Magneto actually does escape along with the rest of them into the Ultimate Universe. At which point you've got a four-color silver-age-inflected, humbled-and-guilt-ridden Magneto with a little trauma-bonded found family of zombie apocalypse survivors and a comparatively pro-human outlook, who now co-exists with a grimdark version of Magneto who, on top of functionally being the Ultimate setting's version of Osama Bin Laden in terms of his singlehanded contribution to the cancerous growth of America's state security apparatus, is an insane cult leader who didn't personally survive a genocide, horribly abuses his children, and who is implied, a couple of times, to occasionally eat baseline humans for fun. So that would be interesting to see 'em navigate