There are tons of companies using mercurial including some of the biggest ones. It's not really accurate to imply that Git won and Mercurial is dead.
I still have to understand how CPython could miss the symbolic meaning of this decision.
Really I think it was bitbucket's total sidelining of hg in favour of git. hg features break regularly on bitbucket and today if you visit bitbucket's home page you're greeted with "Bitbucket is the Git solution for professional teams"
If you look at the outside contributions that both projects get, this is pretty obvious. Hg is getting big changes from Facebook, Google, Mozilla, ...
Maybe the answer to the argument that a paradigm change is needed to unsettle git is simply "monolithic repos".
Git has at least an order of magnitude more people use it, and there is a significant and growing ecosystem around it that mercurial does not have.
Mercurial is not going to 'die' until the developers abandon it; you can still use and install it. Hell, even cvs isn't 'dead', and the last stable release was in 2008.
Mercurial will also continue to 'not be dead' for the foreseeable future, and people will use it for years to come.
...but it is already niche, and will increasingly become so.
Only time will tell, but I'd be shocked if you don't see more big name migrations away from hg over the next year or two.
People are important.
When your project forces them to use tools that don't like or don't know, they go else where. The impetus to change gathers more slowly in companies; but when you see announcements like this, like google code, like atlassian marginalizing hg, like cpython... it's crazy to suggest that it doesn't affect the way people think about mercurial.
Also it's not true that a lot of forward-thinking, progressive, thought leader tech companies are using Lotus Notes. That is true of mercurial.