Those machines are designed for aesthetics not for power crunching

the cooling systems are not designed at all for that kind of use
 

it is quite possible the gpu overheated and was permanently damaged.

best thing to do is not tell anyone what you did. Delete all signs of bitcoin off of the machine and then walk into your boss's office wit a puzzled look on your face "gee boss I dunno what happened"


Theres a good chance Apple care will fix the repair but they may try to weasel out of it if they knew you were bit mining with it.