Once again you post nonsense. Not all Retirement Visas need to have health insurance. We are still waiting for the proof of your pals having to show 500k on entry with the DTV. PS: it is 65k per month if going the income route.
The rules are that you must stay in the country you applied for the visa until it is processed and you have the result. If it is found you have left the country, you face the prospect of having your application rejected/cancelled. However, I am sure there are others that have done exactly what you are suggesting 🙂
I have not seen anyone posting they were asked to show this at a port of entry. If they were they would need to show the classes were booked, maybe by a letter from the school and a paid invoice.