For long stay I would have to travel back to my home country, or be able to get an SETV in a neighboring country. Flying back is not advisable due to my health (I have pulmonary fibrosis and therefore a weak immune system, and fell sick twice after flying before). That's why I'm considering it.
As I said, from what immigration told me I am relatively sure that getting a 30 day extension before amnesty or after is immaterial, because the amnesty since April would have covered that period of time anyway. If the "valid until" date is until July 31st, it will not be possible to use that visa for reentry. As for a 30 day extension, you're right, it should be possible if you always have the right to do one with every entry. That's a situation I've never had.
OK I did indeed get a 30 day extension out of my last entry stamp. What they told me is that not being able to do a border bounce does not qualify for right of entry. Normally one can enter on the "valid until" date, get 60 days, and extend these for another 30.
As I said I HAVE an METV but it IS expired because I could NOT do a border bounce before the "Valid until" date. So I asked immigration if that qualifies for another extension once the amnesty ends, because I could not do a border bounce. They said no. If that is true for me, I am quite sure this is true for everyone whose METV expiration date is until July 31st. If you don't believe that, verify with immigration.
If your METV "valid until" date is AFTER July 31st and if borders reopen, it is possible to exit and reenter BEFORE that date. However, if the borders do not reopen before that date, it is NOT possible to extend the METV inside the country. I have one myself, did border bounces before, and asked immigration about this.
I asked my doctor about that but I don't take medication right now. I only have to take very strong antibiotics if my lungs get infected (for instance by CoVid) and would be almost certainly under supervision. That's the irony, if I get sick, I'd get an extension but wouldn't be able to apply for it 😔