When the cab went silent, it would have been handy to have an ohmmeter to see if the impedance was proper. Certain wiring schemes will do completely dead if one speaker goes out.
Also, without an ohmmeter or doing the battery test, there isn't much reason to take the speakers out. I am guessing that one speaker went down and the circuit is therefore dead. IF you have the speakers out still and want to use a 9-volt to test, be sure not to make extended contact. Holding one battery lead to one contact on the speaker, quickly brush the other battery lead across the other contact. You should hear a light pop and see the cone move. If that is the case, that speaker will work. IF you find one speaker that doesn't 'pop' or move, that is your problem.