georgette I agree there will be a moderate brain drain, also we will struggle to recruit the best academics due to this uncertainty.
However, this thread is about moving to preserve your right to be an EU citizen, as nothing was stopping anyone moving to the US/Aus/Canada before or after Brexit.
I value being European, and the only upside for me of being made to feel unwelcome, is my children's dual passports, which I am extremely smug about given like I say, the mild 'go home' stuff they have had to put up with and general feeling of not being terribly wanted, despite us paying huge amounts of tax over the past decade or more.
But realistically, whole families have moved from Eastern and Southern Europe because there are few jobs and work opportunities there, we know loads. There are much more in Northern Europe, as you point out. I don't think they are all going to get up and move 'home', much as the xenephobes might wish, as they made an economic decision to come here, and will make an economic decision about where is best for their families, and that's as it should be.
If you go stropping off to mainland Europe in the belief that everyone there loves the EU and is super-tolerant of immigrants, this is a completely fallacious belief. I have family in two other European countries, and their right-wing is stronger and immigrants more directly targeted and openly despised by the local population (as I say, 'certain' immigrants groups in particular).