I might also suggest using the autopilot on a basic wings level mode for a while (so long as you can trust it and you know it's in good working order).
I fly a IFR equipped PA28 with no backup equipment (except the GNS430 for navigation purposes), but if I had an AI failure in IMC I'd be keen to get out of it ASAP. It's OK to use the DI and the Altimeter for straight and level, but trying to chase the VSI is something I think you have to avoid doing, and in my opinion using the T/C for long periods of time is a recipe for disaster (though actually maybe the longer you spend getting used to it in IMC the better you will cope with it's waywardness).
I have had an AI go before, and a DI, though not together, and not in IMC luckily, so I am a little sceptical about any kind of hard IMC. Plus my total IMC hours over 7 or 8 years is not particularly high and I tend to fly IMC when there is a relatively high cloud base to be on the safe side.