Who owns the building? I'd go through the channels until you at least ascertain that they aren't baiting, but trapping, and that an exterminator has tried to find the dead rodent. In the venues I work at, I'd talk to the theater manager about it (which means calling during business hours) and asking about pest control efforts underway. If your company owns the theater, go through company managment.
But, all that aside, for what it's worth, sometimes you can't find the dead animal and there is nothing to do but wait it out. The Union and OSHA aren't going to rip out the theater walls for you. You have my sympathy if that is the case. I had this happen at my house and my husband and I stayed at a hotel one night because of the stench. Multiple exterminators could not find the dead rat (but did find another live one) and they said it's common for rodents to die in inaccessible places, because they seek "safety" when they're ill and dying. Which is why trapping is better than baiting.