Britain was of course stupid to Leave (maybe maybe maybe Parliament or even the Scottish Parliament will find some workaround to put a stop to it still?) and Britain should be made to pay when they come crawling back, come what may. They were already half-assed members, enjoying benefits of EU membership but with all sorts of carve-outs insulating them from EU responsibilities and still whining and insulting and mucking things up all the while. One hopes there will be less toleration of that nonsense when Britain comes back like Oliver with its gruel bowl in hand begging for more.
You know, neoliberal and awful though the EU is, and yes of course it is, it is less so than Britain to my eyes -- consider the greater, not adequate but greater, progressivity of taxation and the more ample social supports in so many of its member states, for example. I know euro-bureaucratization is a drag and even tyrannical at worst, but to see that to the exclusion of seeing that implementation of environmental, health, education, labor, safety standards and civil liberties is actually a rare, precious, fragile emancipatory triumph is much more a blindness than an insight.
Brexit is also, of course, one more wake up call in a decade of wake-up calls to Europe that austerity threatens its stability and exacerbates dangerous right-wing political formations (in France, the Netherlands, Italy...) and one would hope they really do wake up this time and finally change course in consequence: especially since austerity hasn't delivered on its promises otherwise anyway. Yanis Varoufakis is someone who is advocating noisily right now for the left remaining in the EU as indispensable to any efforts to radically democratize European politics from within, a position with the broad contours of which I agree, whatever my specific disagreements and distaste for the digirati-broleftist Assange-to-Zizek tinge of his milieu (check out the DiEM25 Manifesto, you'll see what I mean, goodish and illish).
Were the EU to make some adjustments away from neoliberalism and toward democratization (more transparency and accountability in governance processes, more shared public investment in sustainable infrastructure and industry rather than mortgages and financial instruments) then the demands it would be in a position to make upon a rapidly marginalized radically under-performing Britain yearning for Bre-Entry would be all the more welcome. The nonsense of the whole notion of a monetary union without a fiscal union might be closer to a solution, for one thing. Reversing current crazy conspicuous wealth concentration even a little bit in Europe, coupled with an effective PR campaign shifting from gross xenophobic politics onto climate threat politics, say, would be worthy work for all the bright brittle eurocrats to earn their salaries with, if you ask me. Many prominent austerians are inflicted with "the anglo disease" and a temporary loss of Britain could be an occasion facilitating such a course correction. A fellow can dream.
You ask: "Whose terms should be more demanding, the Brits' or the Eurocrats'?" I say Europeans should be more demanding of Europe, and Europe should be more demanding when Britain tries to crawl out of the hole they've dug. Till then, one hopes the left takes up this opportunity to push for our agenda (that agenda in a phrase? sustainable accountable equity-in-diversity) as the right most certainly will do. But I fear the usual inertial professionals (well-meaning and otherwise) looking to cash in while the usual passionate and righteous activists squander the moment in purity cabaret will either break our hearts or muddle through according to something like an historical coin toss.
I'm a dumb American, of course, so what do I know about Europe? It isn't modesty but honesty when I say the obvious -- I'm an interested but inept outside observer, anybody is better to ask about this stuff than me. In this moment I will say the US looks much better off: We went for inadequate but real stimulus not austerity in 2008 despite the GOP and have stuck to weak tea variations of the same. The Obama coalition outnumbers our dim dupe racists providing better chances for comparatively sane national outcomes. The American version of Brexit is old straight white bigots dying of old age in an ever more diverse and secular society. If HRC wins -- blah blah monster blah blah evil blah blah notwithstanding -- the Supreme Court may become reliably liberal till 2050, corrections to jerrymandering if Dems stay organized for the midterms may lead to Congressional representation in line with actual voting results, and then quite a lot can change quite quickly after years and years of too little changing too little (the first years of the Obama administration provide a narrow glimpse of the pragmatic possibilities): We can have more public investment, more progressive taxes, sustainability and harm-reduction policy-making can be prioritized and yield virtuous circles, all the while the country approaches majority-minority diversity and then this ridiculously lucky stupid criminal pack of infants get yet another shot at blowing our chance to do some good in the world.