If they are the principal investors they can manage the investment as long as they remain on the payroll and are involved in the major decisions. But if they want to completely liquidate the business, then yes, they must go home. Lets just say you told INS and or the Embassy that you intended to work for X employer. If you quit, just have a good reason that passes the laugh test. No required period, just be reasonable.
Lets leave it at that.
I am a Canadian citizen. I have recently applied for a job in the US doing the same thing as my job in Canada. I have been offered the position. I have already filled out an ETA 750 and an I-140. But I found out later that an I-129 is what I should have completed.