Follow the RA not the controller
The RA in that TU154 case was overridden by the crew choosing the controller command rather than the TCAS RA. There really is only one case in the vertical where you cannot obey, a GPW takes precedence. Flying at max altitude is the other case. Even there, a climb and stall is to be preferred over not taking the RA.
TCAS III would have allowed RA's in the horiz plane as well, and would be a good alternative to the GPWRS precedence that we have today with vertical RA's