Your extension based on marriage and associated reentry permit was extinguished the moment your divorce was granted.
Since you are 71 and Thai health insurance may not be available to you (from the 16 approved Thai providers) I suggest you apply for a 90 day Non O visa from the Thai Embassy in DC, then apply for an extension based on retirement in Thailand.
The substantial interest penalty depends on the bank, but it is typically all or most of the 1.5 - 2.6% the bank would have paid you in annual profits.
If you leave the money in for the full year as agreed, then you retain all the interest.
A reason for this includes that the banks may purchase high yield US treasury bonds, that also have a one-year term, with your funds.
For the finance or lingually challenged, interest is paid annually on fixed deposit accounts… somewhere from 1-2.5%.
The interest can be withdrawn at any time.
With regard to the ฿800k principal, you can withdraw it at any time, however, there is a substantial interest penalty for early withdrawal, as well as immigration implications, especially if you go below ฿800k or ฿400k depending on timing of your visa renewal.