I had one snap when changing console bushes, but thankfully it was one of the 2 smaller diameter bolts. The bolt on my car hadn't turned much before it galled, then with surprisingly little torque the head snapped off.
To get the bolt out on my car, I removed the longitudinal subframe part, turned the bolt back into the subframe (as if doing the bolt up) using a stud extractor, and then when sufficient bolt was showing through the subframe I welded a nut to the bolt. I then cut off the section of bolt I'd damaged with the stud extractor and used the newly welded nut to turn the bolt and extract it from the subframe.
Thankfully the bolt on my car had galled due to corrosion / dirt on the upper face of the subframe, so the thread damage was very very limited and probably only about 1/10th had visible marking. I ran a tap through to clean up the threads, then fitted the console bush with new bolts.