Nissan, Renault and Mitsubishi are all part of the same group.
It makes sense to rationalise production and markets around the globe. It’ll be a big kick in the nads for the Sunderland plant if the powers that be shut it down.
However, don’t forget that although a relatively small area geographically, the UK is outside of Europe and there will still be a market for compact, right-hand-drive cars. The same cars that can be driven in Japan, Australia, New Zealand, Singapore, South Africa and so on. None of which are in Europe either.