It's a shit question.
"Remain a member of the European Union" is ok, you know what is being voting for - and, equally importantly - the people who voted for the other option also know what its proponents were voting for.
"Leave the European Union" is utterly stupid. Nobody knows what it means. For some leave voters it means stop immigration at all costs. For other leave voters it meant "continue the free movement of people and goods within Europe".
Compare this question with the 2011 alternative vote question:
At present, the UK uses the "first past the post" system to elect MPs to the House of Commons. Should the "alternative vote" system be used instead?
"alternative vote" was defined https://en.wikipedia.org/wiki/...
Imagine instead if this question had been:
At present, the UK uses the "first past the post" system to elect MPs to the House of Commons. Should a proportional voting system be used instead?'
I would expect that this would have carried. Much like the EU question, the alternative to the status quo is a shifting target that can be defined to whatever the proponent wants. Of course, had that question been asked then we'd then have had a mess to sort out when everybody wanted a different PR system.
What should have happened is that DC should have negotiated with Europe on, say, Britain adopting the Norwegian model and leaving the EU. Once he'd got approval then gone to the country with
"Remain a member of the European Union"
"Adopt the Norwegian model of membership in the EEA"
(Or he could have gone for a no-free movement of people or goods WTO rules model alternative)
Now the question is clearer - and even if it had gone against DC, at least everybody would have known what was going to happen.
Britain is utterly crap at negotiating. We have an adversarial system, both in parliament and in the judiciary. Most European nations have had much more experience with having to establish coalitions. It's going to be interesting to see how the next two years go and whether the press is reporting how those "evil Europeans are ganging up on us" when almost certainly none of them are arguing for what they really want but instead for what they understand they can really get.
At least for some things in Europe we used to have a veto. That gave us a lot of clout - however awkward we were we couldn't be completely ignored (and the 10-12% control of the vote helped too). We also tended to hold the balance of power in Franco-German differences - so neither country to afford to upset us too much. We're giving all that up. That might mean Europe now tears itself to pieces or it might mean that Europe can now rebuild itself stronger in a more cooperative model.
We've now got idiots saying that any deal with Europe should now go to another referendum. I predict that there is NO deal that can be made that will attract a majority of the votes. The single largest minority is probably "remain in the EU" which has already been rejected. I suppose we could put two deals on the referendum and force people to chose one or the other - just make sure that the other option is so bad that it cannot win.