If Britain were to exit look for Scotland to bring back a referendum to leave the UK. The Welsh may soon follow. The border area between Northern Ireland and Ireland (which is still in the EU) will become problematic. Britain will lose all those subsidies rom the EU and will have to negotiate a new Trade Agreement which will be on less favorable terms than being a member. Washington may pivot to Berlin as Great Britain becomes Little England.
Brexit is led by the racist UKIP and Boris Johnson who from the 1990s was anti-EU for the wrong reasons.
I don't think Brexit wins today. Britain will remain.