If you mean the small bolt (10mm hex head) beside the VSS, that only holds down the clamp. You can still try getting the VSS out. Aside from the clamp, it is held in by the friction of the O ring in the middle of the VSS against the hole in the transaxle. But corrosion has likely occurred between the aluminum transaxle case, and the aluminum base of the VSS. I know its in a tough area to reach - but soaking it with penetrating oil, then grabbing it as close to the bottom as possible with vise grips pliers, and working the pliers to try and 'turn' the VSS housing, is one of the two techniques I would try. The other one is to use a wood chisel (not a real good one) & drive it in, between the top of the transaxle case and the lip on the bottom of the VSS.
A combo of these two got the first one out that I had to deal with. On mynext Escort, I had to quickly/carefully heat the transaxle case with my oxy-acetylene torch, and still do both of the above. In that case the tran saxle was out of the car (to get a new clutch). Being out of the car made it much easier to work on, but the VSS was still stuck in there really hard.
When I put them back together, I had a coating of an anti-sieze compound on both the VSS and the transaxle. I would think the VSS would stay put, even with the clamping bolt broken off, but I havent tried it.
Good Luck!