30 month period starts when Medicare eligibility began (withdrawal of premium from SS check). If they lose primary coverage through no fault of their own, Medicare becomes primary. i don’t think that the coordination of benefits continues across payers (e.g., if they get another job and another insurer or go on the exchanges), I think they are now just in Medicare Fee For Service. You want Medicare as primary, it’s better coverage even though the dialysis providers don’t like it because Medicare pays less than private.
They can’t “drop Medicare” unless they pay back all SSDI amounts and unenroll in Social Security Disability Insurance. Plan to either remain in Medicare FFS as primary or switch to Medicare Advantage. I’m not sure you can get supplemental coverage (medigap) as an ESRD patient, or if you do it’s probably experience rated so you pay a ton.
Talk to your state health insurance (ship) organization. Everyone else has something to sell you.
https://acl.gov/programs/connecting-people-services/state-health-insurance-assistance-program-ship