In a sense it can be said that it never ended, but it is very clear that level of violence decreased dramatically after the Good Friday Agreements (and for some time before that as well). If the agreements had never happened, or never worked (for example, no real disarmement occurred) and the main armed factions (as opposed to relatively fringe groups) kept political violence as an open option, in principle you'd see an ongoing actual low level civil war.
It's hard to see how this could be allowed to go on. Britain as a whole had been absolutely sick with the entire matter for quite a long time (since the seventies, arguably) and the European Union would hate an actual civil war, even if a low level one, keeping going in its territory*. The US would also very much like the problem to go away somehow.
* IOTL, the role of the EU in making the downscaling of violence possible was probably not fully appreciated. It shows now, sadly.