Once the I-140 petition is approved (14 days), and I-485 is pending for 180+ days, and employee can easily leave to another employer, it only takes them to file couple forms like transfer of H1B and transfer of I-140.
So the most you can keep the employee on a leash is ~2-3 years which happens to be median tenure at tech.
the immigration discourse is filled with false information, and for this reason I prefer only immigration attorneys discuss the matter as they are the most qualified of all the quirks and nuances of the US immigration law.