The prospect of Airbus leaving has been around ever since BAe sold out to EADS. Airbus threaten to leave the UK every time they want a government loan. Now what they're doing is simply lobbying for their best commercial interests - if we crash out of the EU next March without continued EASA membership, things will be difficult for Airbus and they don't want anything to disrupt their business, which is understandable.
In the long term, there's probably an on-going assessment of whether wing production can be done more efficiently in France or Germany. If one day they move, it won't have much to do with brexit - more because the Beluga operation is too expensive.