In a funny way, it seems that Brexit had a net positive effect for the EU. I remember that prior to it, there were quite a few other anti-EU movements in France, Italy, Greece and other countries. It seems that, after the Brexit disaster, they all receded. Even Hungary and Poland got rid of their anti-EU governments. The EU is stronger because of Brexit, not weaker.
The UK is a dynamic, innovative country with a with a lot to offer as a member of the EU, or at least as a very closely associated ally.
The reason that Brexit was successful in quashing other exit campaigns is that the EU was basically forced to take on a super combative, punitive posture with the UK to show other members why it'd be better to stay.
Europe would be much much stronger right now if the EU and the UK could more closely cooperate and align with eachother without both sides worrying about how it'd 'look bad' if they got too chummy.