No influx of ex-pat pensioners. They'll continue drawing their pensions - state or private or both - and stay where they are. Well done the remain campaign though, in succeeding in convincing you that millions of Brits in the Costa del Sol and elsewhere will all come flocking home to flop into...
Nonetheless, if the vote is to leave, Northern Ireland, along with England, Wales and Scotland will leave thee EU. The OP's lack of understanding of the difference between Great Britain and the UK is not pertinent to the facts. Brexit includes Northern Ireland.
Agree with the sentiments, but the question of whether we can sign European players really isn't a reason for voting one way or the other - there are far more important considerations.
Will Brexit affect who we (and every other club) can sign? Que sera sera, I guess.