Yes I think they will still teach it for several years to come. I still think its valuable, although some of it will depend on whats negotiated (single market etc).
It could even be a golden time for EU lawyers as we will now have two systems to advise on.
There should also be a demand for lawyers knowing how to deal with commonwealth jurisdictions, with the prospect of many new trade deals on the horizon.
just do the subjects your firm tells you to or you enjoy or you will get good marks in.