1) What will happen if everybody attained enlightenment and break free from the rebirth cycle? There will be no more humans and animals on earth?
If everybody (including all extraterrestrial life forms) attained enlightenment, then the universe or universes would cease to exist.
This comes from my belief that consciousness is NOT an emergent property of materiality.
Consider the newest proposed principle of quantum physics:
If a measurement yields no information, then the system being measured has not been disturbed.
Conversely, if a measurement yields information, then the system being measured has been disturbed. What is information, other than something that is cognizable by consciousness. A rock doesn't recognize or understand what is information. Consciousness is thus the cause for the collapse of the quantum wave function (system being disturbed).
A universe without consciousness simply doesn't exist. Nothing ever collapses. Nothing ever materializes. Everything is in limbo in the primordial quantum ocean of infinite possibilities.
In Theravada Buddhism, enlightenment is defined as the "going out" (like a burning flame) of the five clinging aggregates, one of which is consciousness.
2) Is karma a Buddhism believe? (if it is, go to question 3)
3) If today I killed a cockroach, the cockroach must have done some misdeed in its previous life thats why in this life it is fated to be killed by me. So how can I be in the wrong?
There are two types of kamma: active and passive.
Active kamma as I understand it is how thoughts/emotions, words and deeds can alter your DNA, which is passive kamma. I believe that DNA is
quantum in nature, and the link between two lives is through
entangled DNA at the moment of death, either partially or wholly.
And so, your killing of the cockroach is not because of the past kamma of that cockroach. It wasn't fated to be killed by you. The fact that the cockroach had a shortened life is not due to its kamma, but by random chance. The cockroach could have enjoyed a long life as programmed by past kamma in its DNA if it had not met you or other unfortunate random chance events.
And so, are you in the wrong for killing the cockroach? Yes, definitely, even if the cockroach has a short life as programmed by past kamma in its DNA.