Letting the UK leave at this stage and state it is in would cause more fallout. Markers would tank further . Civil unrest the UK divided. On verge of implosion no longer united.
The EU gain so much by fixing this.
The UK has fucked itself by listening to the wrong voices. Choose to leave out of ignorance.
EU salvsging it all. Will greatly boost their standing in the world
There's no way EU can force a solution though, not when the whole issue with Euroskeptics is sovereignty, and the country voted as it did.
EU is mostly counting on UK coming back pleading on its knees for a free market deal similar to the statu quo (but with loss of many privileges, and certainly nothing that the Leave camp wanted), so that EU can look benevolent but also can say to other sceptics "see ? they thought they wanted to leave but reality caught up".
As a non-European, I'm curious about something. Why are so many people in the EU in love with this idea of one big superstate? How does that embrace diversity or sovereignty? Seems logical to me that forming a big superstate and the consequences of that in such a culturally diverse part of the globe would be the eventual elimination of diversity. Why do some countries want to part with their identity? It all seems so twisted. Why wouldn't you all be better off being your own nations, with your own currency, and your own laws? Is the goal to just become the most powerful kid on the block? You'd probably all have formal alliances anyway in military situations.
A large and mostly impossible question but still.
Not that many people are "in love with this idea of superstate" actually. It's a very divisive idea, even among pro-EU politicians.
There is a will of unity and growing importance of Europe, maybe even more to be relevant politically and economically against the rest of the world, than for peace and stability within Europe (although the latter is certainly a major benefit, but most people will forget our tendency to get at each other's throat after so many decades of peace).
The main reason some people are favorable to a federal model is more practical than ideological : it becomes less and less realistic to have 27/28 countries discussing and bickering every time a new crisis arises or a major decision has to be taken.