RVSM airspace is very generic, if you are not in an airway but in a direct routing to a waypoint, instead, you can't but keep tracking to it.
It is mainly a comms problem. Solve it by relayed messages to ATC to obtain a revised clearance, then comply with it.
If the comm problem is a lost comm (radios inop) then that is your main problem and you have to keep last assigned FL, etc, etc... even if you are not RVSM. Or would you carry out a specific airspace contingency procedure (such as NAT, for instance) to go off airway then descend to non RVSM flight level knowing that you cannot establish radio contact with anybody?