I haven't heard anything specific for comm fail in RVSM. The general rule
2. Adjust level, speed and proceed to your destination according to the current flight plan route.
applies regardless you are flying in RVSM airspace or not.
But the rule says about flight level from the
filed flight plan instead the current FPL. The level adjustment should be done after 20 minutes in non-radar environment or after 7 minutes when under radar ctl.