This is far from the first project to move from hg to git; many people probably just generally expect that to happen upon any source code management change for anything still using mercurial, which has already been effectively dead for most people for years.
My point doesn't really dispute that hg is dead "for most people" whatever that means, it's just that what the hg people could point to in the past was firefox, but now they've lost that example. Now, we can surely say it is dead.
To be frank, I know of no other major project that used hg. In fact, I think firefox was how I learned about it in the first place many years ago.
