Fortissimo
It may or may not be a good reason for leaving Europe, but at least outside the EU we would be able to go it alone if desirable for UK plc. The USA, China, Turkey & ex-soviet block all operate outside EASA effectively, as far as I know (and probably some in the Middle East as well). I don't see why UK plc can't re-join them. It would most likely be desirable to harmonise with large parts of the EASA system, but that would be a choice, if outside. Bureaucracy is necessary in the modern world, but it needs to be proportional and cost effective, if not, dump it!
If EASA is too complex to roll back to a UK system , then dumping it and going alone seems a good choice.
As for Ireland, we shared the airspace long before EASA was born, we can do it again.
UK licences from PPL to ATPL were accepted before EASA, in most Countries around the World. Its nonsense to say they would not be accepted again – however, I am speaking as a FAA licence holder here.
I hope we at least take the first step and leave the EU.