On the other hand the UK used to be kind of a watchdog of the EU so that role might have to be filled by either someone else or one can hope that the EU politicians will have enough pressure from their own countries.
Lastly even though the UK is in the process of leaving, basically all the politicians responsible for it have either back paddled or just quit. The UK might yet fall back into the fold, only this time without their special status.
They're making such a mess, I would not be the least surprised to see the DUP withdraw support and a surprise election result. The Labour conference seems to be moving them towards a second referendum.
18 months ago I thought claims "it might not happen" foolish, now I'm starting to think it might not happen. :)
Also there's no way the rest of EU is going to accept for UK to stay in the EU with the same privileges as previously (non use of euro, tax exemptions...). Especially since UK was one of the most critical members, now EU has more incentive to move forward.
Personally I can't see how UK can rejoin the EU without applying from scratch like Serbia and so on.
It's vanishingly unlikely in the time remaining, but I would not be surprised to see huge amounts of flexibility magically appearing, if the UK somehow gained a different administration supporting remain or a second referendum. Even at this stage.
Both Junker and Tusk have repeatedly stated that they'd be happy to cancel the Article 50 negotiations at any time and let the UK stay in the EU under its current terms.
The EU will not be stronger after the UK leaves.