if you have no evidence indicating a direct blow to the fork
such as deep scratch or other mark where the fork impacted something

and the crash did not involve a front end impact like slamming into the back of a parked car
then the fork is almost definitely fine

as for what the shop mechanic and his boss told you
the boss not only benefits directly from the sale of a new fork
but probably also fears liability if he tells you it is safe to ride and he is wrong
while the mechanic doesnt worry as much about lawsuits and lawer fees