I'm very sympathetic to the concerns that people like bose-x express. There is so much rubbish out there spurred on by amatuer dramatists. As many have already suggested the option to transfer the admin of your licence to another EASA state is an option, now! The Dept. of Transport (CAA), who will ultimately decide, in truth, will find it hard to refuse a UK citizen the issue of a UK licence based on a current held EASA ATPL/CPL/PPL licence, having previously forced the UK pilot down that path in the first place.
Although you cannot hold two EASA aeroplane licenses you can of course hold as many non EASA licenses as you choose. How these would be maintained is the relevant question.
It is true the EU parliament sans the UK will have the final vote but that in the main is irrelevant. The real work is dome in the working groups made up by representatives of all members. The working groups are constituted primarily by relevant professionals although I'm told some countries do send politicians to these groups. So, if the UK remains in EASA it will hopefully continue to influence.