Originally posted by geiger In dark environments aperature settings of f1.4 to f1.8 is needed to reduce the ISO to an acceptable value. In addition to that a shallow depth of field if mostly wanted for event photography to focus on the main moment which the photographer wants to capture. I guess hyperfocal distance is more related to landscape photography in which the focal length is small and the f number is huge...
My first comment is that you are shooting flash and don't need wide aperture to assure a reasonably low ISO with the Metz 58. My second comment is that f/4.0 (or even f/5.6) is plenty wide for subject isolation* with the 24x36 format and will allow the bride's face, the leading aspects of her gown and the toast to all be in reasonable focus as well.
As for dealing with available darkness with AF, a request might be made to raise the house lights. If your camera can't "see", neither can the guests or the service staff. As suggested above, reverting to manual focus technique is always an option and worked quite well back in the days when events were shot on medium format non-AF cameras.
Steve
* Assuming an extremely dim venue, the contrast between the flash-lit subject and the background should provide adequate isolation all by itself, if indeed the camera will even capture any of the background.