Unfortunately, in most cases Medicare benefit
Unfortunately, in most cases Medicare benefits do not apply to medical care provided outside the US. I would suggest you assess your healthcare needs, and the medical costs in the country you will be retiring in. Depending on which country you plan on retiring in, you may have a public health care system available to you. You should also look into the availability and cost of a private health insurance plan for medical expenses incurred in other countries.
Usually, once you have moved to a foreign country, you're no longer eligible for Medicare benefits (although Medicare does cover residents of Puerto Rico, Guam, the U.S. Virgin Islands, American Samoa, and the Northern Mariana Islands).
However, if you come back to the US, you will still receive Medicare Part A benefits. (Anyone who qualifies for Social Security, and is 65 or older qualifies under Part A.)