Beyond having a grandfather born there (which gives me bragging rights every March) I'm not an expert on The Troubles.
That said, I suspect that the IRA's renouncing of violence has little to do with with Islamist bombings and the like (the IRA were getting weapons from Libya in the 80s, so they're comfortable with Islamic-linked terrorism).
There was a great article about six months ago (about the time of the robbery/bar killing - and I can't for the life of me remember where) that suggested that the IRA leadership (Gerry Adams) has wanted to do this for a while, but couldn't do it previously without getting a lot of blowback from the rank and file, cause more splinter groups, etc.
With the killing in the bar, Gerry Adams had the cover he needed to make the move, and this is the fruition of six months of negotiation with the other six members of the governing council (or whatever it's called).
More cynically, the organization could feel that as it now has $50m in its coffers thanks to the robbery, it can achieve it's goals through a massive political campaign through Sinn Fein and doesn't have to resrt to violence...
Well let's face it, Gerry has always known exactly which way the wind blows . . . Slugger and their commenters are all over this story, if you want another Irish weblog to read.
Labs, Labs, Labs. The GWOT acronym is inoperative, the very first casualty of the Global Opposition to Rogue Groups of Anti-Secular Militants.