Yes, they need to go back.
Why should our kids take an advanced degree program when the job prospects have been destroyed due to H1B cheap labor?
Do you have data? I think L1 Visas are cheap labor, not H1Bs. H1Bs can go to any other job in the U.S. L1s are trapped in their job, they would need to upgrade to an H1B to go somewhere else. And I think L1s are unlimited.