Bring on the catastrophe! It's amazing how much fear can be whipped up. We could still yet retain membership of EASA, but if we don't... Guess what? We still have exactly the same rights within Europe as anyany ot ICAO country. Our licences will still be ICAO licences (they just won't be EASA anymore) The concept of an EASA licence is a joke anyway - in theory you can use it on any EASA aircraft - in practice Ryanair will only accept an Irish licence!
The bottom line is that passengers are still going to want to fly, so the same number of aircraft and pilots will be needed to fly them. Maybe the Reg will change, maybe they won't. Anyway, there are bigger things than aviation. Brexit is supposed to be about bringing back democracy and boosting the economy.