I'll take my UK company home to Germany at the end of the year. No need for a base in a non-EU-country.
Its amazing that you know what the terms of the exit deal that Britain and the EU will negotiate under Article 50 already.
In all likelihood the UK will join the EEA and retain free movement, but even if not, economic migration will still be encouraged and a visa system will be in place, just as the country has for the rest of the world.
My girlfriend is Polish and has lived and worked here for 7 years. She's never claimed benefits or anything.