No. He's saying he doesn't want to do anything at the bank that has them check his passport so his account isn't closed. The account has not been frozen.
You are talking about a rule that DOES NOT EXIST. Show me the rule from the BoT that says tourists cannot have bank accounts. There is no rule. The banks have made that decision to protect themselves.
They would not have accepted your application if it would be rejected. So it will be approved, it's just a matter of waiting until the date on the stamp and returning to get the full extension.
It doesn't matter if it's completed in time. When you apply for a marriage extension you get an "under consideration stamp" which is a temporary permission to stay in Thailand until your extension is processed. Normally it's about 1 month for marriage extension.
You can apply for a marriage extension until the last day of your existing permission stamp. Then your consideration period allows you to stay until they complete processing your extension application.
A multiple re-entry would not help you. The visa only gives you 3 months when you enter Thailand. Getting multiple re-entry will not change that your permission to stay in Thailand only lasts for 3 months. You need to get a 1-year extension and the re-entry permit on that if you want it for long term.
a visa does not guarantee you entry into a country. A visa just dictates how many days you'll receive if you're allowed to enter. Entry is at the discretion of the immigration officer, same as every country.