If I am remembering my comic lore, the Brotherhood of Evil Mutants will be led by Mystique for the next couple of decades. Magneto does have a villain arc before the 90s, where he sets up shop on what is clearly an Atlantic Rl'yeh. Still, for a good chunk of time, he'll be leading the X-Men (or more specifically, the new mutants) before deciding he wants to be a villain again, building a new Asteroid M and leading the acolytes (I haven't read up to then so I am kinda confused why he turned evil again).At some point facing Magneto and his brotherhood and bitter/cynical Null just going "no, wait, he does have a point, let the man cook.. how much genociding mankind we talking here exactly?" would be hilarious..
So, Null will have confrontations with Magneto, but the majority of the time will be when Magneto is Null's boss, which is hilarious when you think about it.