I don't see it happening anytime soon. To rejoin, they woukd have to accept all the new rules, one of them is adopting the Euro as currency. I'm not sure the English voters would be willing to abandon the Pound. Scottish, Welsh an Irish, maybe.
There's more to just losing the pound than cultural attachment (though that's very real) it would also limit the UK's ability to dictate their monetary policy. Mind you ~25% of the EU don't use the Euro, not least of which is Denmark which has a similar opt out to what the UK used to have.
Not that I wouldn't welcome UK back (under equal conditions to all new-joiners, of course), speed-running is not something EU is capable of. Nor is UK. They will not like having to accept the same deal everyone else has to when they had a lot of exceptions for everything. It will take ages before some kind of agreement is reached.