The best this is to protect yourself and equipment as best you can, and at all cost don't get involved. The owners of the establishment have the obligation to deal with the problem, not the karaoke host. So if the problem doesn't include you, the best thing to do is step back and don't make yourself part of it.
Last time I checked, carrting a firearm into a bar anywhere in the country, with blanks or otherwise is illegal unless you are permitted to carry it. Not real smart to intimidate a guy with a gun with blanks who might feel compelled to point his at you, and I doubt theirs will have blanks. Frankly it concerns me that anyone would even consider this as an option.