Mathematics applies insofar as it can model the subject under discussion. It's a great tool for, dare I say, 99.999999...% of practical problems. But mathematics is an imperfect model of objective reality that cannot resolve metaphysical problems like Zeno's paradoxes [0]. Any discussion of retro-causality is inherently one of the philosophy of space and time, which is the domain of metaphysics, not mathematics, so we can't necessarily apply familiar mathematical lemmas to resolve the problems it creates.
Mathematics still apply.