Its not up to the UK. Its unlikely the EU would let them back in so soon, and if they did the UK would be in a weak bargaining position so they wouldnt get all the opt outs and exemptions they had before. Also EU progressives seek greater integration and the UK was the loudest voice against it. Its a lose lose.
As its been 8 years from the vote and the paperwork still hasnt been figure out, its probably going to be another 20-30 years until things have simmered down enough that people can objectively look back and say it was the worst decision in modern history without people getting all pissy and defensive (most of them will have died of old age). Then they can apply to join again.