Peugeot 407 power loss and died while driving

Never known a starter motor to cause loss of power and car to cut out . Grabbing at straws and struggling for an answer to that , could only suggest a wiring fault or a dead short in starter affecting electrics . But with todays cars , anything possible .Might add my garage was AA appointed and I could tell you some tales of AA wrongly diagnosing cars recovered and brought to us in years gone by .