Pros and Cons not taking Medicare Part B?

This really isn’t a question I can answer for you. It depends on your personal situation, health, and financial situation. Your FEHB brochure, Chapter 9, explains how your plan coordinates with Medicare.

Since Medicare is not available overseas, I know a couple of people who have not signed up for Part B. This is in order to avoid paying a fee for a service they can’t use. The downside would be if they return to live in the US at some point.