Medicare does not provide dependent coverage. You may want to delay your retirement so that your spouse will be able to remain on your current insurance as your dependent. Or under the federal COBRA program, your wife would have 18 months of continued coverage. If you live in California, she may be able to have an additional 18 months under the Cal-COBRA program. (If your employer has fewer than 20 employees, Cal-COBRA will be her only source for extending your work-based coverage.)
COBRA is expensive. You’ll have to pay the entire cost of the plan’s premium plus a 2% administrative fee for federal COBRA and 10% for Cal-COBRA.