what would have happened if the pilot had refused to follow the instruction?
Would not happen. No matter how unhappy pilots are with instructions they will not refuse unless there is a very very (safety of aircraft etc) good reason not to.
With the world as it is I believe any pilot refusing air traffic commands (assuming under a control service) would find himself/ herself in a whole lot of trouble with a few of our majestys finest as company until they landed.
Happy to be corrected if wrong though