OF COURSE MARVEL MUTANTS WOULD BE IN MAD MAX'S WORLD. It makes a horrific kind of sense: the mutants have survived so many other tragedies and disasters (though sometimes needing to massively rewrite history to do so, like in Days of Future Past); they've already been dealing for decades with a world that hates and fears them; many of them have superpowers and would be more likely to survive in a post-apocalyptic hell-world; they've been to Australia; and come on, it's just cool.
GET ON IT, FANFIC WRITERS. It'd have to be fanfic, of course, as Warner Brothers makes Mad Max films now and Marvel and Warners don't work together. So no one can make money off of this, but PLEASE LET THIS HAPPEN.