The British state would gain more power to reject EU regulations, but the free movement of capital and labour between Britain and Europe based on long entrenched mutual interest would necessarily endure.
The real fear is that a British exit would encourage anti-EU movements of the right and left across Europe leading to a potential breakup of the eurozone and EU. But some reason a cosmetic Brexit and modest rearrangement of relations within the free trade area could help contain those pressures.
There’ll almost certainly be movement in this direction whatever the outcome of the referendum and any short term fluctuations in the market.