IF you're willing to take a gamble, have your mechanic replace the timing belt anyway and see what happens. Ive seen many interference still work after such an incident, it is however still a gamble because the chance of losing the money to change the belt and still have the engine not work does indeed exist.
Upto you, but last I recall, German motors arnt cheap. Its a gamble id take vs doing an entire R&R of the motor right off the bat.
edit: As for the belt only lasting 27K, you're right. There is also a good change whoever installed it goofed, thay should last at least 60k in Audi's, ive even seen them go over 80K and beyond. Unless something else inside failed, etc. that caused it to snap.