Er, we technically depend on a few persons now. If the servers were to crash irrecoverable and backups didn't work, we'd lose everything as well. Point is, I don't think this is much of an argument either way, though there are pros & cons for both.
Phab will keep running as long as we keep it running on our servers. Also I saw there were efforts to fork it.
AFAIK none support SVN, unfortunately. And well, it's true, but it'll also keep all its security flaws (if any) & its general slowness & never get any new feature.