Perhaps it might be better to pose the hypothetical question in terms of, say, a hitherto undiscovered UK-sized country about ten miles off the West Coast of Ireland with essentially the same economic structure, somehow, despite being unaffected by 40 years of EU membership...
It's a difficult question to answer, I think, and criticisms of overthinking I always think are unfair. "Everything should be made as simple as possible, but not simpler," is one of my favourite (possibly apocryphal) quotes, attributed to Einstein. In this case, it seems to me that the answer to the question, "Would I vote to join the EU from outside?" depends, at the very least, in which country I am living in, what terms can be expected, and what attitudes the country has had as a whole towards the very concept of a European union.
I'd like to pose an alternative hypothetical question, if I may, although this might be better off in a separate thread. Assuming that the UK left the EU, and it then turned out that the dire warnings of Project Fear turned out to be (at least partly) true, how bad would things have to get before Brexit supporters regretted their decision? Is there *any* level of consequence that would persuade you that maybe it was wrong to leave the EU?