. You are correct if it’s an extension based on marriage, but with one based on retirement, the third option is, you can combine monthly income and funds in a Thai (sole) bank account.
. Are 100% sure of that? When I was in that position, I’m sure I was told that the divorce nullifies a visa/Extension based on the marriage. BUT, I must say that Immigration were not at all interested when I enquired and did tell me to deal with it upon normal expiry date. I just thought they were using common sense/practical solution.