The thing is, most people will just stay, and the freak behind Freenode will have numbers to back up his claims, that his "community" is strong. Who knows how many of those users just keep running irssi in screen or have it configured on bouncer, checking it once a year when they need to ask question. Maybe over long time, the numbers will shift. But most people just don't care about the platform they chat through.
Also, yes there are lots of idle people but at the same time when nobody responds to them with ~50ppl to the room, they will eventually wonder why.
Plus channels having no op (Just chanserv), maybe freenode staff. Which will look even weirder than usual.