In my opinion, the EU needs the UK more than vice versa: it has spent decades stumbling from failure to failure, both economically and politically, and has very few member states with support strong enough for it to count on. Attempting to punish the UK now would be suicide.
One reason the EU stumbled so much was that there was one large member country that opted out of many of the bigger EU projects. Maybe with the UK gone, it will be easier for the EU to get things done. But it's more likely to lead to a complete disintegration of the EU with more countries leaving.
