It has not disappeared, nobody is claiming that (not even the guy you're replying to, if you read again what he wrote). But it has shrunk considerably. "Convincing evidence"? It depends on how high you put the bar, i.e. if you'll be convinced by a thorough survey of all (ex) Gnome users that won't happen any time soon.
My personal anecdotal evidence (= every Linux user I know has moved to something else, like XFCE, after Gnome 3 was out) plus all the comments (thousands of them, some quite ... energetic :) by people disapproving of the new "philosophy", plus a surge in alternatives (Unity, MATE, Cinnamon, and see the current Nautilus-forking fest) is enough to convince me that Gnome is indeed losing its existing user and developer base, that the Linux desktop is now much more fragmented than it was just a few months ago and that it will stay that way for quite some time. Unfortunately.