Over at Slugger, they are discussing an alleged proposal from the UDA that the government give it £1 billion to end its campaign of violence and convert itself into a legal organisation. At one level, you'd be forgiven for spitting coffee on your keyboard at such shameless blackmail. But there is a valid point here. What do you do with a private army when its time has passed?
There are a couple of historical courses. One of them is to integrate it into the regular armed forces of the state. This has been pursued by among others Finland, France, South Africa, Zimbabwe, and the Republic of Ireland itself. The degrees of success vary widely. De Gaulle took the decision to disband the Resistance and recruit its members into the regular French army in August, 1944, thus avoiding the possibility of a private army continuing to exist after the war and also putting an anchor out to windward against any other generals wanting to be king. He was probably also concerned that a Resistance persisting into the postwar would be essentially communist, just like it had been during the war. However, having lost power, he found that his future political career couldn't do without the Service d'Action Civique private intelligence service/goon squad.
Finland chose between two rival rebel armies, one nationalist and one communist, had a brief civil war, and then had some trouble integrating the remaining communists into the new army, not to mention more trouble between the German-trained Jäger and the rest, but eventually managed it. South Africa decided to integrate the ANC's bush fighters into the old SADF as a new National Defence Force, which worked out at least in the sense that there was no trouble. (It worked out far less well in terms of force readiness, and released a troublesome population of mercenaries onto the market, though.)
Zimbabwe had one of the worst experiences of this kind. The ex-Rhodesian army, ZANU-PF and ZANLA were all meant to be merged into one British-trained army. General Rupert Smith describes what happened after that in The Utility of Force, which I promise I'll get round to reviewing. The British advisers suggested that the new force should standardise on the Rhodesians' equipment, as this would mean ammunition would have to come from the central arsenal, and therefore any violence between factions could be shut off by denying it bullets. The Rhodesians refused to hand their arms to their ex-enemies, and so the force was built up with the Soviet-type weapons the guerrillas handed in - for which the ammunition was widely available on the black market, and which the parties held illegal stocks of. This meant that the ZANU was able to form another brigade (the 5th) outside the terms of the agreement, with which it proceeded to crush the supporters of ZANLA.
Eire, having had its civil war, suffered problems with the heirs of the contending parties (the Army and the Citizen Force) for years, although it didn't amount to a serious threat to the peace. So, it can work, but a) it's difficult and b) the requirements are complicated. In Northern Ireland, the reaction of the Republicans to a proposal to put more UDA men into the army is something we can all do without. (Not to mention that the Royal Irish Regiment is being reduced in strength.)
Another option is to demobilise it. This requires the consent of the demobilised just as much as integration, and they may have security and/or identity concerns that call for some sort of successor organisation. It also places a challenge on society to reintegrate them, not least to create jobs. A notable example where this was done, proved difficult, and eventually succeeded is Israel.
There's also the option of permitting the organisation to live on in different form. The UDA seems to be aiming for a mixture of 2 and 3, turning itself into some sort of non-armed political entity and paying off its soldiers. This one doesn't have a very good record - disarmed freikorps and einwohnerwehren were the first organisational underpinning of the Nazi party, and rearmed pretty damn quick whenever it was asked of them. And the Kärntner Heimatdienst in Austria has been a nuisance ever since its creation.
Sometimes, though, there are only the options people let you have.