The following quote is from Alan Jamieson talking about "Post-church groups":

But they are not static places. The people in these groups have no desire that the groups should become institutionalised like the churches they have left. Rather they are groups that exist for as long as they are meaningful and helpful to the core group of people who make them up and give energy to them, and when that ceases then they end. That ending is not seen as failure, but as the opportunity for members to form - or link up with - other groups, and make other connections with people of like faith.

Seems to be pretty much what's happening with THIRD, except that we are privileged to have a "post-church" group within and with the backing of a church!