When Wikimedia's servers go down, freenode will
still be up, so we can at
least get updates still. If we hosted it, it would go down with the site.
There's nothing stopping us maintaining an emergency channel on
freenode for that kind of thing. Of course, if the IRC channel is run
on a different server than the rest of the site, it's not likely to go
down at the same time (it would require the whole cluster to go down,
which happens occasionally, but not often).