P0135 code A/F Sensor S1 Heater Circuit

After having my catalytic converter and two O2 sensors replaced (they had been cut out / ripped out and stolen), both the Check Engine Light and the Orange Triangle/! Light will not stop shining. The mechanic hooked it up to their computer and a P0135 code is the result.
Prior to the damage from the theft, my CRV was in perfect working condition. There was no evidence of any sort of pre-existing malfunction. I did drive it after the theft because I could not leave it where it was and, also, to drive it to the mechanic. All told, I put fewer than thirty miles on it before it was repaired.
Insurance is refusing to pay for a mechanic to further diagnose the reasons for the warning lights unless it is a direct theft or, possibly, a mechanical error. The mechanic can't offer an estimate without doing diagnostics. I am cash strapped (like many!)
So, my questions: a.) Is it safe to drive? B.) Am I damaging my vehicle? C.) Is this related to the theft of the catalytic converter/O2 sensors? D.) If so, how can I prove it? E.) If not, what needs to be fixed/replaced? F.) What questions should I be asking both the mechanics and insurer? G.) Is this damage typical after a theft of this sort? H.) Do I need to repair it at all? I.) Will I pass an emissions or safety inspection?

My car may be an older model, but with less than 50,000 miles on it, it should still be in excellent condition. I am very concerned and, just a little, worried that I am being treated unfairly. I have little faith in insurance companies.