Catalytic Convertor Lambda Probe

UK Audi 100 Avant 1991 2.0 litre 5cyl fuel injection RT engine.
The exhaust down pipe is in need of replacement, and the catalytic convertor
looks, ermmmm, rather delicate. I suspect its flange will not survive the removal of the damaged down pipe.
Owing to its age (like me !) I do not feel the car warrants the expenditure on a new and expensive catalytic convertor.
As I understand it, in UK, a car of this age does not *have* to have a catalytic convertor, nor does it need to pass the more stringent *cat* emissions test for MOT test.
Now, the audi parts catalogue suggests that there is an optional straight through pipe as an alternative to the catalytic convertor.
Alternatively, as with my 1989 (non-cat) saloon, there is an exhaust system that comprises down pipe front box centre box rear box
as opposed to down pipe catalytic convertor centre box rear box on my avant
The systems seeming to be identical for the latter two components. I am thinking of obtaining replacement down pipe and (non-cat) front box. This would make the exhaust system look like my 89 non cat vehicle.
However, the "cat" car has a lambda probe which is fitted to the top of the down pipe upstream of the catalytic convertor, so the engine control system is obviously different.
I appreciate emissions will increase, but what other consequences need I be aware of?
What actually happens if the Lambda probe is disconnected ? Does the engine revert to some non lambda mode of operation, or does it totally confuse the engine management ?
Searching google I found a thread where someone split a cat open, discarded the innards, welded it up again and reported "No problem". It could well be that my 13 year old cat is worn out in any case, so I may not in practice be increasing pollution.
Any information / comments gladly received ...
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