If Ubuntu died, we'd still have the other Debians. For myself, I stopped installing Ubuntu a long time ago and just install Debian. But Redhat is responsible for a helluva lot of core technologies in Linux, and while I find some of their conduct a little irritating, Redhat getting out of the Linux game would have serious implications.
Ubuntu is eminently expendable. I tossed it out of my organization three or four years ago and have not missed it for a second.