Explanations:
3mice's cashflow issues were well documented, and though Kukubo left, the company is still running(I think its his sister running it)
Ushahidi is not a business. It's a fun ride for a noble cause and once a proper exit shows up, you take it. For a leader of an open-source company, a job at Google is one of the best exits you could get. By that time Okolloh had built Ushahidi into a 2million dollar company, with a flourishing asset base(iHub and NaiLab), so her leaving does not mean Ushahidi is dead
In the case of DotSavvy, to be honest I did not know that Kemibaro had left, and I don't think its true. Verification needed