It is NOT difficult to fly manual at higher flightlevels. The controls are more sensitive but any (professional) pilot will be able to maintain altitude and heading etc. For flight into RVSM airspace, the rules require the autopilot to be used (and servicable).
When receiving a TCAS resolution advisory, you do NOT change course but follow vertical commands like "climb climb" , "descend descend" etc.
If the autopilot fails in RVSM airspace, you fly manual (maintaining altitude!!) and get a reclearance to a lower, non RVSM flightlevel.
If you cannot maintain altitude, ie engine failure, then you turn away from the airway (usually 45 degrees course change) and start your descend. In this case you will make a distress call and try to get formal clearance.