....does this mean I won't be able to go and work for a European carrier coming out the other end of it?
It depends entirely on the final decision on Brexit. If the UK maintains some agreed position of membership/compliance such as that 'enjoyed' by Norway, Iceland and Switzerland then nothing will change. However, if the final decision is to cut all ties with EASA, the UK becomes a "third country", just like the US. If there is a transition period, this would be the time to transfer your state of licence issue but bear in mind the "Nothing is agreed until everything is agreed" and it is still possible that we will reach the so-called cliff edge on 31 March 2019. This being the case, there is now less than 11 months to be
certain of obtaining an EASA licence with a UK-approved ATO.
However, IMHO the chances of the 'cliff edge' scenario are about the same as Brexit being entirely abandoned and it is more likely that some weasel-worded compromise will be reached. The whole Brexit farce will have cost billions and the UK will have gained nothing but lost its seat at the decision-making table.