One problem is that there is so much variation in what constitutes a "folk club" that the term does not provide a useful guide to what you will find when you go there.

I have gone to clubs which are pure concerts with a booked guest and booked supprt act and I have gone to clubs which would in American terms be called "song circles" where people really do not want an audience at all.

If any audience drops below a certain critical mass (both in total numbers and in turnover) then the club is on its way out. It may be possible to turn the situation around but that requires a lot of hard work and dedication. Usually it is better to recognise that it is time to move on.