The answer to that question is simple and plain that if the amazon forest get burn then there will be natural catastrophic events all over the globe as these forest are considered the LUNGS of the world and if something happen to the lungs then all system in that case whole ecosystem will started to collapse and when they will reach the threshold then whole planet will go BOOM with different natural disasters.
Thats what will happen if amazon get burn. But thats a big IF so ....
It not suddenly take affect because we have a supply but of course when the time comes we can feel it by the huge number of oxygen given off by trees that's why the population take a lot of oxygen but we have a limited supply so it can cause from people to die, not immediately but their lives become shorter.
even if the whole amazon forest disappeared/burned down the oxygen supply is never the problem because the oxygen produces by amazon forest barely leaves
the forest because the oxygen is almost up by the species, organism, microbes etc.. that are living there(like I said at the first page of this thread). the main problem
we would have is that the trees in amazon forest absorb Co
2 in the atmosphere and without the amazon forest the CO
2 would remain in the atmosphere
and will contribute to a faster climate change.