United Kingdom

It would be politically a disaster for literally everyone on both parties, nobody would survive the cull. It would also be extremely questionable democratically speaking. That said the Brits know for a fact that the Leave vote won on nothing else than lies, the public there are too apathetic to care, or at least the ones that do are not in enough numbers or have enough influence to make a difference. I doubt these new allegation will be welcomed any differently if I'm honest and I also doubt the claim in the post above that without cheating the result would of been different, they had a thirst for it and the result would of been the same. With hindsight however I do believe the result would be different.

As for the UK's status they still are a full member(or as full as they have ever been) and will stay like that until March 29 2019, on the 30th they will enter a 21 month transition period till the end of 2020 where they will still be in the EU but lose any decision making capabilities and the like.
Presumably at any time during this period they can reverse the decision whether by parliament, have another referendum if they like or just say "Sorry chaps, this was a shit idea and we have changed our minds".
The decision then would be with the EU as the process has already legally started as to whether they would accept that and what conditions they would place on the rogue nations re-acceptance.