Going to old company

[ind140]

Hi,
My friend came to us on Company A (H1B)visa.
He transferred his visa to Company B from A.
After few days he applied for visa to company C from A. He got Visa with company B first and joined with B. After few months he go his visa approval thru Company C and he joined Company C. Now he want to go back to B.
1) Is it must to leave the country and reenter with Company B visa.
2) If he want to go for dependent visa (H4)
thru his wife what is the procedure.

Thanks in advance