No one knows what will happen as no one can know. It's never been done before but the UK would have two years to sort things out.
I am more than likely to vote IN for the very selfish reason that it will be easier on my clients investments in the short term (markets don't mind good or bad news but hate uncertainty - so it makes my job easier), but I don't like the way the EU is going and feel here as good a place as any to forward my view.
I'm a europhile by nature, I'm in favour of free movement of labour, immigration doesn't both me in the least, but an unelectable Federal European Government is a ghastly idea and I hope for a close vote to spook the Germans into shying away from further Federalist Union.