One thing that nobody mentions in the Medicare-for-All discussion, is that Medicare as it now exists is not exactly single-payer! 29% of people signing up for Medicare select a private Advantage plan. 17% buy private MediGap insurance. 15% have Medicaid. 33% have employer or military supplemental coverage. (numbers don't total 100% because some are older than others.)
That's about 90% that have something beyond true single-payer government Medicare! So I think the private insurance companies would still be doing that even with Medicare-for-All. Does Bernie not know this?