As an aside, Dirac's statement is so interesting because 1) the angular momentum carried by such a field configuration is independent of the distance between the electric and magnetic charge, and 2) it only requires one point magnetic charge to work.

So as long as there is at least one magnetic monopole somewhere in the universe, his argument works.* What if there's genuinely only one? It's an interesting scenario to think about in terms of the limits of the scientific method; for example, if that one monopole passed through an experiment and left our Solar System, never to return, that experiment would essentially be non-repeatable and therefore non-verifiable.

*in a classical universe; not sure whether GR or QFT impact this statement.