Time to kickstart(er) a new project to prove them wrong, then ? Just like double-fine was being told by publishers that Adventure games were a thing of the past.
I'm mostly interested in the realistic WW2 online combat genre, which seems pretty dead. The only things around I know of are Warbirds and its cousins WWIIOL and Aces High. While all of them appear to be actively supported, they all date back to the last millenium.
Well... I've been involved quite a bit with World War II Online, and they are not exactly growing by miles and bounds. The customer base for a hardcore sim seems a lot smaller than for more arcade-style games, so I don't know how you get funding for a large, complex piece of software with quite a limited payoff. I'd love to work on it, though...