Strangely Airbus, whilst a European company, sources a considerable chunk of the parts for its aircraft from outside the EU. General Electric make many of the engines which power Airbus aircraft. GE is er.. a US company and the US has no trade agreement with the EU. But Airbus is perfectly capable of using US manufactured components.
There is a big difference between what company bosses say they will do and what actually happens in circumstances such as this. In my view there is no way that Airbus will quit the UK. It has far too much investment tied up here (in both its aircraft and space divisions) and has continued to announce further investment even since June 2016. It is very spooky that both the boss of Airbus and that of BMW (who make that iconic "British" car, the Mini, in Oxford) announced their veiled threat on the very day that a number of people gathered in London to demand a "Peoples' Vote" (which, in case they have forgotten, was held on June 23rd 2016). Pure coincidence, I'm sure.