During my CPL training, my instructor failed the gyros, and as we were above a layer of IMC we shot the ILS proper partial panel, in IMC. To make things more complicated, just as we entered the cloud (stratus layer about 3000' thick) he failed an engine (ME aircraft). It was bloody tricky keep the aircraft right side up, trying to identify a dead engine in IMC with no gyros, with the TC wobbling from side to side like crazy as my rudder pressure varied is next to impossible.
These were sudden post-it-note "failures". We experimented in a Sim afterwards, with the instructor flying the "aircraft". We gave him a slow vac failure in IMC (and a few other failures
) which almost ended in 'disaster', and probably would have in a real plane....
EA