Back in the days when men were men and sheep were scared, I always thought the military had some salient points to teach us and one of these involved limited panel instrument flying. I will never forget the gradual failing of an AI (in the simulator) and the way in which I was still drawn to information, even though I knew it was incorrect. The solution was SO simple, yet immediately effective; cover up the affected instrument. Now I know I'm teaching you all to suck eggs. We ALL know this and some silly old git, waxing lyrical about the 'old days' doesn't help, but sometimes a gentle reminder might be useful. In this particular instance I slapped a bit of paper on the glass, held in place by a good dose of tongue lickage. Straight away that instrument is no longer compelling and you're forced to start scanning the performance instruments, just as you've always been taught. It actually becomes significantly easier as the old training kicks in.
After that session in the 'box' I managed to procure some of that non-sticky, sticky plastic (you know, the stuff they use for sticking on car windows to keep the sun from burning your bits) and cut it to fit the AIs and HSI. Fortunately, I never had to use it for real but did have cause to drag it out again in the simulator and it works.
This is, perhaps, related to the accident in question but not at all a comment on the pilot's handling of the event. As you know, spotting the failure is the most difficult part, as often the indications are insiduous and can be masked by other factors; being bumped around in turbulence being an obvious one. However, once you do notice your AI is knackered it is important that you ignore it and that's why I bore you and insult your intelligence by relating my obvious yet, hopefully, useful reminder of the uses of a bit of spit, licked onto a piece of paper and stuck to the offending instrument.