I plan on removing my cat along with the AIR system, but what do i do with the O2 sensor going to the cat? Just cut the wires and leave it? Or put the O2 sensor in the pipe that will replace the cat? At least i think its an O2 sensor lol i haven't looked at it closely. Ive searched the forum but i cant get a good answer.

I don't think there is an O2 sensor there. There wasn't on my car, but of course I haven't seen every third gen.
I believe there should only be one in the DS exhaust manifold.

There is no O2 sensor behind your cat. It will not throw a code.