Will, you stated:
"I wonder what would happen if the UK Government actually decided to relinquish dominion of Northern Ireland and hand it completely to the Irish Republic. "
I suppose I do as well and a civil war may possibly have been the result, but that would have been resolved, one way or another by the Irish, without British influence, years ago. From that they would have moved on. Festering wounds, on the other hand, have caused much more pain over time!
I have often wondered why Britain so freely gave Honk Kong back to China ( a much more repressive regime) but would not relinquish Ulster to a democratic Republic of Ireland? In Hong Kong's case they did not poll the people as to their desires but acted against the wishes of what was no doubt a majority. I suspect that the hope for monetary gain in Chinese trade exceeded any respect for democracy! Shit happens, especially when political corruption is the driving force!