I agree with duff on this, at least on the FM part.

You can replace it with something better, more damage, or resistances like fox said. you'll get +450 hp from warmogs passive still so you're only losing 250 hp. which isn't much in exchange for a some decent resistances, or triforce which is a little of everything.

Having lots of hp doesn't make you a tank. It just help you survive a bit longer. Plus, late game. Armor & Magic Resist > HP

I think if you swap Warmogg's with FM and replace the Mallet with Triforce you're lookin at a pretty mean Xin Zhao.