Meh, taking petty revenge doesn't make sense from a diplomatic stand point. The fact is that both the UK, and the EU have a lot to gain by trading with each other, and sharing regulations. Refusing to do that is cutting off your nose to spite your face.
Dealing with countries like Orban's Hungary is easily doable by taking a much more nuanced approach than "once you leave you're done".
For example, the UK would hopefully learn its lesson about leaving because before they left, they had a privileged position, with vetos, and the ability to opt out of implementing certain regulation, and not being part of schengen, and opting out of the €uro, and ... By leaving and rejoining (if it ever happens) they will (presumably) lose all of those benefits. If they were to do it again, and prove themselves to be abusing the mechanism, I'm sure the penalties would become much more harsh, and people would become much more reticent to let them back in.
Long story short - most diplomacy works best by taking a nuanced, and in general, forgiving approach, not by blunty applying rules like "if you leave you never get back in".
Of course... I might be biased in all these. I'm a Scot who voted to stay in (like most Scots by a wide margin). I of course very much want it to be possible for us to rejoin.