While I think anything is possible (the British did give Hong Kong back to the Chinese after all) there are a number of issues here which make this more complicated.
We are after all talking about a conflict which began in 1169, at least in the case of Northern Ireland as us been complicated with Reformation Religious politics as well as land and class issues ever since.
Also many Catholics are very happy with NI being part of the UK - tax situation and health care is better (cheaper).
Yes if NI wants back into the EU it has to mean a break up of the UK - remember the official name of the Conservative Party is the Conservative and Unionist Party. Brexit was/is British nationalism - giving up NI would lead to a Scotland referendum.
Finally Sinn Fein (at one stage considered the political wing of the IRA) just won the second largest number of seats in the Republic of Ireland elections - that frighted a lot of people in NI - so older battleground positions are being taken up.
Do I think that there could be a vote at some stage - yep - but respect for all groups in order for peace to continue has to be a bigger priority.