I don't think they're dependent on the UK's membership of the EU that much.
First, there's plenty of people not from EU who participate in European research on European grants. Think Russians in CERN and so on.
Second, secession from EU doesn't mean freedom of travel will be thwarted for scientists. UK was already not on Schengen, so what? At worst they'll have get a visa every few years.
In short, that person might consider that his son will figure it out.
Regarding "kind" - "kind" is irrational. Rational is often not kind and kind is often not rational.