Setting up a healthcare for all/medicare for all plan could work best that way.
Right now, those on medicare alone really don't get great benefits unless they happen to be very healthy and have very little actual use for it. Getting into a supplemental plan during annual open enrollment for the vast majority provides the most bang for the buck. Getting into a BlueCross/BlueShield, or Humana or other 3rd party handler that's a HMO or PPO that also adds in certain features that case-by-case beneficial such as vision, or dental, or prescription drug plans, all available at MUCH lower monthly cost plans than what it would be without Medicare.
Allowing businesses to continue to provide tailored programs for their employees using the same model seems the smartest way to go, and best of all worlds:
1. Allows employers to setup the same, or even better structure they have to their current plans now, at a MUCH lower cost to the employers and employees since most of the benefit coverage will now be handled by the federal program.
Amount that the employer has to pay goes down. Amount that the employee has to pay goes down, and may even be incentivized to no employee payment paycheck reduction at all. co-pays and annual deductibles will go WAY down for the vast majority even if kept at the Medicare plan levels.