According to some opinion, that won't arise. We'll still be part of EASA. My comment was directed at separating commercial aviation from non commercial.
If EASA are to continue their supervision of UK airspace then no doubt they'll want to charge for their expertise. This they can do from commercial sources. The 'minnow' that is GA can be left to the administration of national regulators.
Apart from anything else, we might then be able to make sense of the present licencing regime - a tangled web if ever there was one.