I am a US citizen retired in Greece and I have a monthly payment of $189.00/month for my Medicare Part B.
Should I terminate my Part B option and purchase instead a health plant from a local provider?
Isn't the Basic Medicare plan to cover my expenses in case that I have to fly over for a major medical condition?
I can't really advise you on that. It probably depends on your future travel and residency plans. Medicare does not pay for medical services you receive outside the U.S. except under rare circumstances (https://www.medicare.gov/Pubs/pdf/11037-Medicare-Coverage-Outside-United...). But, if you terminate Part B coverage, you will likely have to pay a higher premium if you decide to re-enroll in the future, and you can only enroll at certain times of the year (https://www.medicare.gov/your-medicare-costs/part-b-costs/penalty/part-b...). So, you will have to use your own judgment.