indulge me for a second. you said you went on "vacation". so why did you leave your car at work in the first place? you thought it was safer there than to park at home? if that was an issue, wouldn't it be safer to just find a friend to car-sit? pay a nominal fee to store your car in their garage or driveway?

either way, my personal opinion is that approaching your boss about this was all wrong. for whatever reason, YOU decided to leave your car at work while you were "on vacation". you had choices and you made that choice. obviously no one expected your car would be scraped, but accidents happen and you left the car there at your own discretion.