You say the pub has "practically no custom" at present, which may be good from the viewpoint of starting folk events there, but is obviously not good from the licensee's viewpoint. They will be keen to get people in every day, not just one day a week. And soon, or they will have to close the pub again.

It sounds as if there might be scope for various musical events on different days of the week - maybe a 'joining in' session one day, a 'singaround' on another, and even a guest folk club type night on another. It will take time to establish all these and build up the regular clientele, but it sounds as if they have nothing to lose by trying. (I hesitate to suggest it here, but maybe they could even have non-folk music on other nights - trad jazz or blues, for instance)

Good luck with it anyway!