Absolutely no change, because should it happen the UK will immediately have to agree to continue with everything unchanged, until there is time to start renegotiating each and every thing that links the UK to the rest of Europe.
The rest of Europe will not be that interested in bothering to renegotiate - offering to accept the status quo or cease trading/flying whatever. The UK will have no choice but to comply...
But, the paperwork will keep lots of people busy for ages!