with all the redundent radio and com systems how common is it for a modern air carier aircraft to be NORDO? With all the cell phones around (in flight bags and down back) can't believe there won't be some com capability.
More likely with smaller aircraft. Watched it from a tower cab one day at a non-radar towered airfield and the pilot ended up with a stuck transmitter, so called the FBO with the cell phone and the FBO called the tower, instructions were relayed and everything worked fine.
When on a instrument clearance the procedure of following the clearance is the one in the book and most likely to get the job done with least disruption and risk, but in the final analysis the FAR 91 applies: "the pilot in command is the final authority as to the safe operation of the aircraft."