Nothing?
Any physician/surgeon who takes any medicare patients CANNOT treat a patient for cash! If he/she does that it's a crime and he/she risks being sent to federal prison.
If any medical procedure has been determined to not be covered by Medicare (the kind of decision that a "death panel" would make) then it is absolutely billable to the patient/family, cash, check, or CC.
It is illegal to bill the patient for a procedure that is covered by Medicare, and in many cases the Medicare reimbursement is very low. But that's an entirely different issue.
If the government wants to have the effects of a "death panel" without the stigma, it could easily say "Yes, we will cover those liver transplants for 90 year olds. But we will only pay the physician $450 for doing the surgery." or "Yes, we will give FDA approval to that cancer drug. But we will only pay $75 per dosage." This may in fact be the way it will come to pass, because then the eeevil doctors and drug companies can be demonized for failure to provide the service.....