I don't think it will vanish, but will diversify and splinter into smaller groups interested in different areas of the sport. Although it will seem like there are less people out I think that it will offer prospective members more options. There seems to be three different camps at the moment; the beginners rides (which I see as the East Croydon ones), the XC epic ones (like the one Rory & co did yesterday) and the technical / DH ones which I try and get people involved with.
We do ride with a diverse group of people on our rides and most aren't in ACC and aren't interested in joining. The way we may get people in through our rides is by introducing them to the more technical riding through ACC and mentioning racing, etc.
I know that some people see the way things are going as the MTB side running down but for those of us who have been riding off road for a few years, I see it as more of a progression in riding ability. It also means that for those people who've started riding off road and want to progress, there is the opportunity for them to move up within the structure of the club rather than look further afield (which I believe has happened before). As competence increases, people become disillusioned with riding around Croydon which let's face it, doesn't really offer much challenging technical riding. If we were to only ever ride locally, I think that a lot of present members would be less inclined to stay in the club.
As I (and a few others) have mentioned, we are now in the process of developing a rota so that there will always be someone at East Croydon station on a Sunday and those rides will be tailored more at both those wanting to get the miles in and at beginners (with easy drop-out points en route, which has worked well before). I can't promise that we'll do a huuuuuge ride next week but I do plan to aim it more at getting the miles in (for those who want to) rather than messing about at places like the Wall of Death. I'll be trying to hurt myself on Saturday at Jedi's North Shore trails instead