As an EU national who came to the UK 5 years ago, I'm in the process of preparing to leave in a year.
Already numbers show that even if the outcome is vague, a large percentage is alrady leaving ( mainly low-wage workers that are affected from a weak GBP )
https://www.bloomberg.com/news/articles/2017-08-24/immigrati...
Now imagine what happens when people realise they'll need a Visa or getting a new passport and rejecting their own. I'd certainly leave. My bet is that a 30~50% of EU nationals will leave within the next 5 years, which is a huge blow to London and the UK.