Foreign residents refers to those foreigners with 'permanent residence' status, not those on extensions of stay who are classed as temporary.
Your the holder of a temporary extension of your permission of stay (a permit, not a Visa) based on retirement. Your status is 'Non Immigrant'.
That applies to all foreigners that entered on a Non O Visa.
Health Insurance 400/40K (not to be confused with the $50,000 Medical Insurance) is required for annual extension for original Non O-A Visa entries.
You don't get any financial assistance from the Government for health care, you simply pay far less in a Government hospital than a private hospital.
Regarding the 'Medical Insurance' of $50,000 USD for entry, there are Insurers who will provide such for being over 75, but the cost will be greater due to the higher risk involved.
Just Google 'Medical Insurance for age 75 and over' for a list.
This topic may be of interest: https://thethaiger.com/talk/topic/4613-need-covid-insurance-longstay-expat-farang-over-age-75/
You'll need a re-entry permit and the period of Insurance must cover the period granted on entry.
If your extension renewal date is for example in August and you re-entered March, the policy would need to cover from the date of re-entry to the extension renewal date in August.
Just to clarify, that was not my implication. From what I've read in the original post, what needs explaining, is why the plane went into a high-speed dive. That suggests to me, either deliberate action by the pilot, or something that was so rapid in onset, the pilots could do nothing about it.