simple test for motors- connect the affected motor's ESC lead to your throttle output on the receiver itself and spin it up from the radio without the APM in the loop. That will tell you if both the ESC and the Motor are working. If it doesnt run properly, swap out a known good ESC and test it again.
AFAIK i dont think youd have much luck keeping a hex stable with a failed rotor. Could be wrong, as ive not yet experienced that but the result of a midflight failure is typically a case of terminal deceleration trauma.