Well, the math is a little beyond me, but if I put off paying for Part B from 65 to 85 because I have remained in Thailand I would have saved around $50,000. That will pay for a lot of months (depending on the Part B premium in the future, I guess) even at three times the Part B monthly premium.
Don't forget, there is no urgency about getting Part B. I can get it immediately on returning to the USA, if need be.
I am fairly certain if I get a serious illness leading to drastically reduced quality of life at 85 it will be suicide for me, but who knows when push comes to shove.
However, I am not averse to being told I am wrong and foolish.