I think it will happen, but a l-o-n-g- time in the future. The last thing the Irish want (and need) is (a) the bill, currently footed by the UK taxpayer, and (b) three-quarters of a million unwilling Unionists, not necessarily in that order. IMHO (northern Prod here) it would be nice if it happened by the centenary of Partition (next year), but, barring some cataclysmic development, there's absolutely no chance of that happening.
And there remains a possibility that it might never happen. After a century, the two bits of Ireland have developed different cultures, and the combination of the two, while respecting what each sees as its rights, could be problematic. The Shinners naturally say there'd be no problem, but then they comply with the classic definition of a fanatic - someone with both feet firmly planted in the air.