Yes, absolutely those must be replaced. They are one time use and can fail if reused, which as another poster mentioned, failure will result in your transmission dropping out of the car.
Damn straight! The common experience has been that those bolts fail about 10,000 miles after the TB job, when the engine/transmission will fall out the bottom of the engine bay, sometimes hanging only by resting on suspension parts, sometimes by landing on the pavement. Either way, not something you want to have happen to YOUR car, especially if it happens as you are at speed on the freeway.
And yes, it happened to me. First time I got the belt changed, the dealer assured me when I called to set up the appointment, that they would replace the mount bolts. When I picked up the car, there was no mention of bolts on the invoice, so I asked about it and was assured that their shop foreman had been to training on the topic and was certain that new bolts were not required. I vowed to buy the bolts and replace them myself, but got busy and you know the rest. When the engine fell out of my car at 10,000 miles and got towed to the dealer, they had to redo the entire TB job because of the damage (they warrantied their work for 12,000 miles, so the job was on their dime).
So, yes, absolutely, new mount bolts, and don't argue with me! Just replace the damn bolts. Period. Job ain't done 'till you put in new bolts.