lets imagine that in all the human in earth become Arhant, so after their death they will not born again (i mean all of the humans). after this will new humans born or Not, will earth become a planet without Humans ?
Not if, my dear friend, when.
Suffering will always exist. It is after all the first noble truth. But I think your question is a theoretical one, and a very good one. Yes, theoreticaly, if all beings now on earth attained enlightenment, then there would be no sentient beings as we know them (born live die). But back to the vastness of reality's expanse, surely another meteor would come around and add new life to the earth before it falls into the sun.... de ja vue )))
Do you think that everyone in this world will develop a sense of dismay (samvega) over the universality of suffering? Of those who see life in this way, what is the percentage that will develop an attitude of heedfulness (appamada) to avoid being duped by types of desires that come our way? How many will have a sense of urgency towards the practice of Dhamma?
What the Buddha has said is patisotagami or against the current of conventional thinking. Buddha knew this well. That is why He said, “Dear Bhikkhus, ones who would not realize this Dhamma is like this earth (in amount). Ones who realize this is like this small amount of soil on my finger nail.”
As per the Teachings of the Buddha, the world will be without humans, but it will take an extremely long time. This is been said by the Supreme Buddha as He can remember the past up to infinite time such as many Sanvatta Kalpa, Vivatta Kalpa, and Sanvatta Vivatta Kalpa. Sanvatta kalpa means the time that takes the world to be destroyed after countless years. Vivatta kalpa means, time of the beginning of the world.
Long before this day is going to pass and in that time of the people with an eighty-thousand-year life-span, there will arise in the world a Blessed One, an Arahant fully enlightened Buddha named Metteyya /Maithree. You may now wonder whether there would be enough food for all. Buddha once said, ““Dear devotee, I am looking at 92 Kalpas (a long time) to the past right now. In all that time, no one had to face any destruction of their families as a result of offering their food.”
If all of the humans become enlightened you still have other sentient creatures who would become humans. At that point those would be saved by buddhas and bodhisattvas. But even then there is not a finite number of sentient beings since there is no transmigration, just rebirth of sankharas which is not strictly limited to one entity. So, I don't see an end of sentient beings reborn on earth. Whether humans evolve into something else is unknown. And eventually the earth will be destroyed by the sun and disintegrate with the rest of the universe.
There are infinite beings in a universe. Event if a large number of beings become enlightened then still there will be infinite beings. The number of beings in all planes who get enlightened is approximately 24 asankya. The number of past Buddhas is infinite, the number of Arahants are infinite as there were infinite Sasanas. But despite all who becomes arahants infinite being remain, of whom some maybe born in this world.