Hahahahhahahahaha

Go read literally any statement from EU officials on the subject. The Euro must legally be adopted by any country which has a good enough economy (exemptions aside such as the UK or Danemark IIRC).

Sweden benefits from a loophole where they legally have to switch to the Euro but haven't started the process yet. However, there is not a chance in hell that the EU would give the same leniency to the UK, both for political (that'd make us look "weak") and financial (the British economy is several times larger than Sweden's) reasons.

The UK getting to keep the pound in a rejoin scenario is a delusion. Or at the very least the political hurdles must be made clear because it is anything BUT given (and should I remind you how the last 8 years of negotiations with the EU went?)