I fly an aircraft with a slightly dodgy Attitude Indicator. Since the aircraft is limited to day VFR in any case, we haven't replaced the instrument, and over the course of a year or so I've got used to it. However, at first, it was extremely disorientating having the artificial horizon doing something different to the real horizon - and that was in good VFR conditions.
Personally, I doubt that very many pilots would be able to recognise such a problem, and then handle it safely, unless they'd seen and done it several times before. When you're that low, by the time you've identified the problem I suspect it would be too late (although in this case, it sounds from what you say of the RT that the pilot did identify the problem). Partial panel work that you do for the IMC rating is not enough, IMHO, because there is no requirement to recognise the failure. The only way this could be taught properly would be on a simulator (or else on an aircraft where the vacuum pump can be turned off by the instructor - and although someone may correct me on this I don't think that's legal).
Just my personal opinion, I don't have any stats or documents to back this up I'm afraid.
FFF
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