FXCM has not just the retail business, but also owns Lucid Markets (institutional fx mm/hft) and Fastmatch. These two alone gotta be worth something. Lucid was pulling in >100mm profits in 2013(i think), and its only a 15 man operation. Also their retail business turned a profit, have established marketing networks and they were the biggest (1.3bn customer assets). They had a viable business.
Alpari UK operated at a loss since years, and together with the new 40mm hole there was just no value there. They had no technology stack worth anything, only Metatrader licenses and Currenex. Also, russians.
The other one that went bust was some small time NZ bookie, i havent heard about any other insolvency.