The Nerdfighters site still seems to be there, on the day it was expected to disappear. I don't know whether that's because the admins have succeeded in getting it onto an affordable hosting plan (e.g. by getting the membership count below 100,000), or whether ning.com just haven't got round to deleting it yet.
I'd be inclined to invite people from Nerdfighters if we can. I don't think it would be aggressive, as long's it's suitably worded.
I think it's worth observing that Exilian's democratic structure means we shouldn't suffer from the same problem. At the moment, it seems to be entirely up to Nerdfighters' site owners whether the site lives or dies - the admins seem to be working hard to give it a chance of survival, but the owners aren't talking to them. I don't think that could happen to us.