According to this (German), UK citizens will keep their rights upon Brexit, in particular the already acquired right to residence and extension of the permit they already hold. It's possible that UK citizens will even be able to come to Switzerland as freely as they do now!
What's interesting is that according to this agreement the UK is to apply reciprocity. Because it is an EU/CH treaty, it won't be enforceable on the UK after Brexit - but without renegotiating the treaty, CH is stuck with it.
What's interesting is that according to this agreement the UK is to apply reciprocity. Because it is an EU/CH treaty, it won't be enforceable on the UK after Brexit - but without renegotiating the treaty, CH is stuck with it.