Hard to see the non Polish eastern euro routes surviving post brexit.
Why are all Europeans going to pack their bags and leave or those who stay never ever going to leave the UK to visit home again?
Don't get me wrong some won't but there will always be demand for Eastern Europe flights. That's also not forgetting that there will be lots of Europeans allowed into the UK even if controlled as the UK have no choice in the matter unless they want to cut themselves out of the single market.