Hmmm
Northern Ireland is weird to drive through, areas especially then were Nationalist or Loyalist so its not as simple as saying Brits leave catholics die.
Several counties are majority Catholic at the time and while the IRA isnt armed at the time without active British support the Unionists will likely lose control of some of these areas, South Armagh, Derry, Newry for example.
If your Catholic in Belfast, well your dead im afraid. If your a Protestant in South Armagh your dead.
British withdrawal drags the Republic in, who are no where near ready to do so but there was a genuine fear the British would withdraw as has been discussed on several other N.I threads. Its a bloodbath across the board and if Britain Does stay out completely the whole edifice will collapse and drag brder areas of the Republic in. While the Irish Army isnt capable of beating the Loyalists it is capable of holding out those majority Catholic areas.
Which is a disaster in of itself as Britain would have to intervene, the PR would be just too bad from the event not to get the Army back in there.