I'd have thought you'd need a sensor in order to ensure that the computer got the right input? With no sensor but with a system designed to run optimally with a sensor, it would be like permanently being in limp-home mode?
The catalyst has no actual connection with the sensor - it's just a convenient bit of pipe to hold the boss. Some models have the sensor in the downpipe just upstream, some I think have the sensor near or even in the exhaust manifold.
Whatever the catalyst does to the exhaust the sensor is always up stream so it can't know about that, so the decisions on whether to remove either the catalyst or the sensor are surely entirely separate. Removing the cat is a purely mechanical one - how do you connect up pipes to bridge the gap - but removing the sensor would need more fundamental tweaking of the control system, seemingly pointless anyway.
Just my thoughts - I've no real knowledge.
