"Have terrorists like the IRA been 'rehabilitated' or have they just accepted the situation while continuiong their 'struggle' in less overt ways?"
I am not sure what you mean by "less overt ways".
You can never generalise about things like this: like I said before, with regard to the IRA, the LVF and indeed any organisation, you'll always get people who recant etc, and others who certainly won't.
For example Father Patrick Ryan, who ran operations for the IRA, has it seems one regret: that he didn't achieve more.
The question of rehabilitation in prison didn't necessarily apply in N Ireland. There was no attempt to do that, and indeed for many, it was a case of banding together and reaffirming their commitment to whatever cause. On the other hand, some found God, and recanted, some read a lot and became more reflective, etc.
Ironically, one of the ones who found God, is the very man now suspected of having been protected by the British state and is still free, but that's more a question of retrospective justice for the victims.
Obvously with the radical Islamic terrorists in the UK jails, questions have been asked about deradicalisation programmes, very understandably. But because there are issues with that it doesn't mean it can't work for some people. Tho I wouldn't want to be the judge of who is genuine and who isn't