Good question. Still hypothetical for me at the moment. Last time I got an O-A, I just squeaked in before any insurance requirement was imposed. The Emirates policy was certainly good enough to get my present sandbox COE, albeit with a visa exemption.
Understood but you will have to purchase insurance for the extended portion, if you want it. Unwise to have no insurance. Personally, I would book my flight presuming an extension and take my chances.
Problem is that, if insurance is included with ticket (Emirates), extending the ticket later will invalidate the insurance. Or rather, will leave you without cover for the extended portion of your trip.
If you can guarantee getting back in before your visa expires, you shouldn't need a re-entry stamp. However, if for some reason, you cannot get back before then, and depending on when your current stamp expires, it may be worth considering buying a re-entry stamp as a precaution. I had to make a similar calculation when I returned last year. Didn't work out for me though, due to the Covid entry issues.
Not true, travel insurance is for travellers, whether on holiday or not. It can last for as long as you are prepared to pay for. I use this form of insurance all the time. I stay in Thailand for 90 days but my travel insurance covers me from departure from UK until my return, certainly more than 90 days total.