Stolen Catalytic Converter

IF it is on a W22 chassis, the engine is a GM 8.1L and NOT Ford. On my W22 there were FOUR O2 sensors. One before and one after each Cat Converter. Some W22 chassis only have two O2 sensors. In any case, these engine have a fairly sophisticated computer system, ECM, that will notice something is wrong if a straight pipe is added, especially to one side only. This can result in a "check engine" light, or in the worst case, send the engine in to "limp mode". On the OLDER vehicles, most of them would get better performance and better mileage with one or both of the cats removed. On the newer vehicles, because of the ECM, the mileage will certainly decrease as well as the performance. Do not compare 70s-80s vehicles with the newer computer systems. Your engine was designed to have two Cats and since you did mention that you have insurance, get a replacement OEM Cat. As I mentioned before, you can probably get a used Cat within a few days and have it welded in place.
The alternative is to pay hundreds of dollars and replace both CATs with a straight pipe and then pay several hundred dollars more to have your ECM recalibrated to not show a fault. Of course after paying that money you will have lowered your mileage and performance.