Sadly no matter what, serious and irreparable political damage has been done to the UK and in some ways to the EU as well. There will be a further erosion of trust in government, likely fewer voting, those that run for office to be more likely racist populist right wingers pushing dreams of unicorns.
For the EU it is actually a big, flashing neon advertisment!
• The EU actually, really
throws its entire weight behind even a small member country if it's being threatened – european solidarity is real!
• The EU can and does act decisively, unanimously and consistently in matters of foundational importance.
• Attempts to divide and conquer
individual EU countries have failed completely.
• The whole debacle is increasingly demonstrating the value of EU membership for the member countries (not least the other members' solidarity!).
• Especially in the Brexit process the democratic principles and actual democratic realities of the European Union have been demonstrated more clearly than ever before, defying the absurd nonsense from the europhobes.
• Myths of rainbows and unicorns outside of EU membership have gone up in smoke at the harsh crash into reality.
• The advantages of democratically legitimized but still united negotiating positions vs. an outside party have been exemplified more clearly than ever.
It's not accidental that all the various "exiteers" in other european countries have completely abandoned their illusionary aims after their claims have been crushed by the Brexit reality.
So while the UK actually leaving would of course remove some important mass from the EU, in almost every other way the Brexit attempt (so far) has actually substantially strengthened
the European Union, both internally regarding its support in and by its member countries and abroad as a demonstration of unity and actual negotiation prowess against a common threat.
For the UK, on the other hand, it has demonstrated that pretty much all all the imaginary claims about the EU (being "undemocratic", "intent on destroying the UK", "inept", "ineffective", "chaotic", "disunited") are clearly proven false, but interestingly all those projections have turned out to be very much real in the UK's own political system and with its own political personnel – and most notably among those who pushed for Brexit the most.
Almost all those problems the EU has been scapegoated for have in fact been perpetrated and/or ignored by domestic UK politicians, and the current chaos is just the result of that recognition becoming ever more unavoidable by now, regardless how many smoke and stink bombs the fanatics are throwing as a rearguard diversion. Their time is running out.