car should be driveable then, but I wouldn't recommend it if it's cut at the header because cold air can go back into the engine and warp things. Also wanted to let you know that there is a primary and secondary O2 sensor. The first one reads stuff and actually does things to change the a/f ratio. The second one is passive and just reads air coming out of the back of the cat. So, if it throws a code, you can wire an O2 simulator into the car that makes the car think that the O2 sensor is getting a good read. It doesn't matter much that it's not there because of the fact that it doesn't really do anything anyway.s

 

but if it was cut right after the cat it wouldnt warp anything? becuase if this is harmful, im sure the seller has drove it for some while with the exhaust cut right after the cat

 

basically if he cut the exhaust off it might be a long loud smelly ride home but itll drive fine, it might use a little more gas but it should be ok to drive....