How would you define "Mechanical damage?" About the only way a plug would be damaged is it was defective (simply replace), there was excessive pinging (assumed you would mention that - but haven't so I'm ruling that out), something like a nut (a screw is usually too long) got in the cylinder, there is damage to the piston pin or crank bearing and the piston was banging into the plug or a valve has dropped and has hit the plug. But in the latter two cases you would probably have mentioned an excessive amount of internal clanging.
All that said, if the engine is turning over (and assuming the spark and fuel are present) the car would likely at least attempt to start and might possibly (assuming no damage to the piston or valves) run, even if roughly. If the engine turns over rotate the cylinder with the bad plug until the piston is near the top. Shine a flashlight into the spark plug hole and see if there is any visible sign of damage. Most likey you would see scratch marks in bright aluminum on an otherwise carbon black piston top.
If you could post pictures of the plug damage, give a more detailed description of the cars mechanical issue - and what you have done it might help to get to the bottom of the problem.