I’m not sure that the fake degree directly has anything at all to do with the Visa. He got the Visa by being sponsored by an employer. I doubt if immigration cares about the degree, or said another way: the degree wouldn’t have been a condition of getting any sort of immigration status.
But it probably does matter to the employer. They can terminate him and revoke their sponsorship. Then the Visa goes away.
The degree is an integral part of obtaining the H-1B visa. If the degree is fraudulent then the visa was improperly obtained. His employer may well be an Indian job shop that could care less about whether or not the degree is real or not. He should try to contact both U.S. Citizenship & Immigration Services (the folks who approved the petition) Immigration & Customs Enforcement (the folks that arrest and deport folks). The third agency created at the demise of legacy INS is U.S. Customs & Border Protection who really don' have a dog in this fight unless he is flying into the country...then they would get involved. U.S. CIS has a pretty active H-1B anti-fraud unit which visits employers to make sure they are real employers, etc....its just a matter of getting to the right person....and being "right" about the diploma being fake.