The Irish Progressive Democrats have voted by 201-161 at their conference to dissolve after all their remaining parliamentarians and the party's founder agreed the party had no viable future. (RTÉ News: PDs vote to wind up political party) The PDs have had an interesting history as one of the most influential small parties in Ireland but also one of the most hated. Maybe it was because they were willing to criticise sacred cows. Or because they got things done. Or because of their tone. Or their mistakes. Historians will no doubt debate it endlessly.
But one point of curiosity struck me. The PDs are dissolving when they are still in government, in a sort-of Jamaica coalition with Fianna Fáil and the Greens. It is very rare for parties in national government to self-dissolve. Sometimes a coalition leads to a fusion of parties, but the formal mergers have generally taken place in opposition as part of a structural reorganisation. But I can think of only three other parties that have dissolved in government, ironically all called National Labour. The British National Labour Party dissolved at the end of the Second World War, but as it was part of an all-party coalition of national unity and I'm not sure if any members of the party still held ministerial office by 1945. The situation for the Irish National Labour Party is another exceptional case as it had broken away from the regular Labour Party in 1944 over accusations of communist infiltration but reunified in 1950 when both parties were part of a grand anti-Fianna Fáil coalition and the National Labour leader James Everett was a Cabinet minister. The Australian National Labor Party never really existed as more than a breakaway group in Parliament due to splits during the First World War who after three months merged with the Commonwealth Liberal Party. Although the product was the Nationalist Party of Australia I'd discount the CLP as the right in Australia has a long history of mergers and absorptions and the result is usually more a takeover by whatever name than an actual merger. (National Labor did, however, have a longer life and organisation at the state level in Western Australia until it two was subsumed into the Nationalists after defeat in 1924.)
None of these are completely comparable to the PDs. The Australian party was really just a vehicle of motion for a political realignment, the Irish party ended by undoing the split and the British party had politically really been defeated in 1940 when the National Government was replaced by an all-party coalition and so was in the unique situation of political opposition but in government.
Are there any other examples I'm unaware of?