In my experience, open source projects that are primarily backed by companies fail to create a real community of developers. Therefore when the company dies, development stalls.

RethinkDB was something that I though would still go strong without the backing. I never used it and was never involved, so I'd love to hear what happened when the company died.

(One exemption is Xfree86 though, which was forked successfully by to community to Xorg if I recall correctly)