People will come back in time, as much as the replay value of a singleplayer game can be (such as Skyrim) it's fairly low compared to the ever changing online communities albiet that everyone has a tendency to troll at least once an hour.
Even with Battlefield 3 with it's online-ness, it's not the same as here, you don't know most of the people you play with and the people you do play with will more than likely include someone from cRPG!
There will be more and more people who will trickle back over time, I wouldn't worry about cRPG failing, sure there will be a few people who won't come back but the regulars who have been playing for a long time, will come back eventually otherwise they wouldn't have been playing for so long. Even if it feels like a commitment, (so much time and effort to get to where you were, don't want to let it go to waste) people will come back.
Just give it time, there was always going to be a drop around the time large titles are released, and two at once (three if you're a console... can't class you as a gamer... errr... console user) then you're going to have a drop off at some stage.
Strategus will keep a lot of the clans around, although I have noticed most of my clan members disappearing from teamspeak, each time there is an important strategus battle at a reasonable time, they're there, waiting and willing to play.
People love the mod, maybe I am being a little bit of a fanboy, maybe I am being over optimistic, but it won't die any time soon. The death will come with the release of a similar game, probably mount and blade 2 where they will more than likely have some form of progressive character online, in which case the commitment for players will severly drop.
I don't think you can expect a massive online game with a progressive system such as Battlefield 3 to hook people for as long as something like cRPG has. I mean, the community isn't quite as close nit, you'll hardly ever see the same players twice unless you're on their friends list, things like that, you're not going to have quite as good a response and therefore time that people will spend playing.
Trust me, people will come back, even if you didn't read this, I sort of lost what I was saying half way through to be honest with you, don't worry, stop fretting, people'll get bored of the other games and will come back, not all of them of course, but the majority will. Mount and Blade 2, if it has a progressive character system, will be the death of cRPG, if I had to bet on it of course!