Short answer: A person whose Medicaid or Extra Help eligibility starts, ends or changes can make a plan change within 3 months of the change or of the notice, whichever is later. That includes leaving a Medicare Advantage plan for Original Medicare or dropping or switching a drug plan.
Under 42 CFR 423.38(c)(9), a person may make a Part D election within 3 months after a gain, loss or change to Medicaid or Extra Help eligibility, or after being notified of it, whichever is later.
Medicare.gov describes the window for someone no longer eligible for Medicaid as lasting 3 full months from the date they’re no longer eligible or the date they’re notified, whichever is later. During it they can join a Medicare Advantage plan with drug coverage or a drug plan, switch plans, drop a Medicare Advantage plan and return to Original Medicare, or drop a drug plan. A separate window applies to someone told they won’t qualify for Extra Help next year.
This matters for D-SNP members: Medicare.gov notes a person can stay in a special needs plan only while they meet its conditions. Losing Medicaid means no longer meeting a D-SNP’s condition, so use this window to move the person into coverage that fits.