To remain the right of EU-EU flights Easy Jet will have to get an AOC in the EU. ( Or use their Swiss AOC). EU Airline must not be owned and controlled by non-EU investores. The planes therefore will have to be registered in the respective EU-Country. To fly these planes by british nationals they must have the right to work and live in the EU. UK will be granted these rights only if they grant them to EU-Nationals as well. But this is one of, if not the crutial point, why the Brexeteers want to leave the EU. So if things really go bad, the big loosers will be the Easy Jet Crews with a british passport. Their planes will move, and they might not be allowed to follow them