As you say “who knows”. What we do know is that if the U.K. government messes anything up, then it’s the fault of the U.K. Government with no excuses of just following Brussels diktats. There are still problems to resolve over the U.K./EU relationship, but no one imagined that there wouldn’t be issues in breaking up a 50 year marriage. We can pretty well do what we want, without interference from Brussels, or without having to get 27 other countries to agree or one of them providing a veto. We are a big enough country in our own right, we just have to relearn how to stand on our own two feet again….
I don't know the answer but maybe somebody knows or knows where to find it but I wonder what the ratio of EU & UK laws we were governed by while in the EU. What I do know is we were not in the Euro, we were not in Shengen so that is two big areas where we still had autonomy, there was freedom of movement but we also had control of our own borders.
I strongly believe that we still could veto some rules and regulations in our own parliament, just like Scotland is part of the UK but does have a certain level of autonomy.
Also, we are not the major player that some would have you believe, it is OK to ask for help now and again. You can't always do everything by yourself.