I agree that it is very hard to say how this will turn out for the UK. For all we know they might "leave" the EU only in name. One thing that is sure though - which also relates to your comment on ways that states interact - is that the barriers that the EU has been removing over the past decades will, to an unpredictable degree, be put up again. I think that removing barriers and allowing the free movement of goods and people has been great for progress in general. Ironically London is a great example of a place that really benefited from the free movement of people within the EU, as so many people from all kinds of backgrounds have moved there. If geography has taught me anything it's that where you are matters, so where you can move matters almost as much.