There's absolutely no need to switch the reason for your extension - marriage to working. Perfectly ok to teach/hold a WP whilst on a marriage extension.
Straight to the airport. Don't get into trouble /arrested beforehand. Make sure you have the cash ready when you arrive at the airport immigration. Cash, apologetic behaviour and you should be fine.
Charge inventing is inevitable :) I know what you mean though. 1000 baht will feed a Thai family for a few days or so. Just chalk it up to experience. Always be on good terms with your employer here when you leave, visa transfer, work permits and an employer reference will still need to be done.
Not really, the clue is in the name, you are exempt from needing/using a visa, so they put a stamp in your passport, a no-need for a visa, visa exempt stamp.
Very sorry for your loss. I flew back to care for my mother in 2016 who also had cancer. I had a very similar experience to you, so much time was wasted, and it went from 'you have two options' to 'several months to live'. We were quite angry. After she passed away, I returned to Thailand to find that my fiancée had run off with a rich Korean guy. Definitely a low point in my life. However, I persevered with my original plans. My mom had told me to 'go and have a good life' - so I did, it kind of honoured her memory as well. I met my wife of five years, built a house, had two wonderful kids and completed my teaching degree which led to my dream job. You can't change the past, just put all that energy that sadness and loss can cause into taking care of yourself in the future. I am sure that it is what Chanpen would have wanted for you. You played a major part in her life. I wish you good luck Tony🙏