A well run folk club will last longer then most, but folk clubs in general are thin on the ground up here in Scotland. The Inverness one closed ages ago, and now there are a few pub sessions, and a bar called Hootenanny, [how Scottish is that?] I would love to start another club, [masochism?] but can't see people coming unless I book big names, and they are too expensive for an average folk club. Not that they don't deserve it, they've been underpaid for years, especially when compared with some mediocre 'Pop' acts. It's all down to how much you need to charge at the door to cover costs, and like it or not folk is regarded as cheap entertainment.
Greg is partly right in the boring guitars remark, but nobody ever got bored with a GOOD guitar player. Good residents, and a firm policy on floor singers also help.
The biggest cause of disappearing folk clubs is the malign influence of big brewery chains, and managers rather than landlords.
John