My motor has been running poopy.

My cousin damaged my o2 sensor about 3 months ago. It throws CEL code #43 (Fuel supply system) everytime I drive about 5-10 mins into driving. I had a mechanic buddy drive it and he said it was definitely the o2 without me mentioning anything about it. The engine will bog and sputter if not warmed up for at least 15 mins. The cars power is about 65-75% of what it used to be. Fuel consumption is ~20mpg. I have driven ~2000 miles since I first discovered the problem.

Ya, I know, I shouldn't be driving it. Money has been tight and I am getting a new o2 this Tuesday. The motor has 89K on it and was running very reliably before the pooped o2.

Possible any damage may have been done that I will now regret to the tune of a rebuild? What do I do from here? Run a compression test?

I appreciate your flames, but somebody got advice too? To pour gasoline on myself, its a B18c1.