Is Nibbana final? Or if you attain Nibbana, can you be reborn again in Samsara if you wish?
Theravada Buddhist Perspective:
After Nibana, can one be reborn again in Samsara?
No, that is not possible. When reaching Nibbana one has destroyed all fetters. One has uprooted all defilements. There exists no longer Ignorance (Avijja) which binds beings to Samsara. One has freed oneself from the cycle of rebirth.
If you attain Nibanna, can you be reborn again in Samsara if you wish?
No, that is not possible. Volition/intention no longer has any potency. Actions no longer bear fruits. Actions become merely "functional" (kiriya) in nature.
Is Nibana final?
Nibbana is final when one has reached the forth stage of Enlightenment, i.e. Arahantship. At that stage the practitioner has destroyed all ten fetters. As a result of that, further rebirth is not possible.
"bodhi and nirvana are hitching posts for donkeys" -- Lin-ji
There is no "before" and "after nirvana". It is timeless and self-existing.
There is no "one" to attain Nirvana or to be reborn and there never has been.
There is no "attainment", it is attainment of no attainment.
Directly understanding the above is called "First Bhumi". This is when the clouds open and the endless sky of Dharmakaya that has always been there is seen for the first time. However, Samsara and Nirvana still remain quite separate in one's mind, and one keeps hard-switching between Dharmakaya and ordinary world. From this moment on, through 10 Bhumi's one grows in ability to bridge the relative and the absolute in practice until the two are no longer two separate perspectives but one fully-integrated and highly-functional unity.
Samsara and Nirvana are not places. It is not like there is a Nirvana-without-remainder universe and a Samsara universe. Also, mere conventional existence does not end with Nirvana.
Using imprecise language I would say something like those beings who have realized Nirvana are reborn in Nirvana and not Samsara.
Although, when we use the word 'samsara' loosely, we refer to a place, strictly speaking, samsara refers to the contaminated aggregates (i.e. the aggregates one takes due to the power of karma and affliction). A so-called Hinayana arhat is free from that samsara.
While a so-called Hinayana arhat is not reborn due to the power of karma and afflictions, he is subject to the 'inconceivable transformation birth' and the 'inconceivable transformation of death' due to the power of the imprints of ignorance. Being subject to the inconceivable transformation of birth means taking up a mental body due to the power of the imprints of ignorance.
In his commentary to 'Maitreya’s Sublime Continuum: The Essence of a One Gone Thus, with Commentary by Gyaltsap Darma Rinchen', Geshe Jamphel Gyaltsen says:
What is called the inconceivable transformation of death is the destruction of the mental body and it is compared to the last of the 12 links, aging and death. It is compared to the presentation of the twelve links of dependent origination of a person circling in samsara. Destruction in general, in the context of an ordinary being of the desire realm and form realm, (formless realm being apart) refers to old age and death. In order to take rebirth after death we go through the intermediate state. If after one week in the bardo, the bardo being has not taken another rebirth he takes another birth in the bardo until he finds a new birth outside the bardo. This goes on up to seven weeks with small deaths and births every seven weeks.
His nirvana is not the final true cessation. In this sense, his nirvana is not final.
A fully enlightened Buddha is free from all types of rebirths. However, he can manifest or show the aspect of being born. We say that Shakyamuni Buddha was already enlightened at the time of his birth as Shakyamuni, but that he showed the aspect of being born... showed the aspect of undertaking austerities... showed the aspect of achieving enlightenment, etc.
The non-abiding nirvana of a Buddha is final in that it is the final true cessation free from the two obscurations. It benefits both others and oneself.
It depends on who you ask. Theravadin Buddhism clearly says “No.” But Mahayana texts say it is more complicated. From my personal point of view, for what it is worth, given the psychological nature of nirvana (given, that is, it is a change in a state of awareness and connectedness and not a great increase in wisdom), a person would need to achieve nirvana a great multitude of times to acquire the wisdom of a Buddha. On grounds of compassion, I suspect, many Buddha-like beings continue to return to samara in order to teach Dharma and help their many friends who remain in samsara. Nonetheless, even if parinirvana is viewed as a heaven for Buddhas (a correct assumption, depending on which texts you consult), the Buddhas there remain connected with people in samsara and remain able to influence them and help them overcome suffering. In my view, those of us who are in samara are in great need of those Buddhas who decide to be reborn in samsara.
According to Itivuttaka 44, after final Nibbana, a living Arahant still experiences the five aggregates, including the feeling of pain and pleasure, without the five aggregates burning with the fires of passion, aversion and delusion. After the final extinguishment (parinibbana), there would no longer be the experience of the five aggregates anywhere.
This was said by the Blessed One, said by the Arahant, so I have heard: "Monks, there are these two forms of the Unbinding property. Which two? The Unbinding property with fuel remaining, & the Unbinding property with no fuel remaining.
And what is the Unbinding property with fuel remaining? There is the case where a monk is an arahant whose fermentations have ended, who has reached fulfillment, finished the task, laid down the burden, attained the true goal, ended the fetter of becoming, and is released through right gnosis. His five sense faculties still remain and, owing to their being intact, he is cognizant of the agreeable & the disagreeable, and is sensitive to pleasure & pain. His ending of passion, aversion, & delusion is termed the Unbinding property with fuel remaining. (Note1)
And what is the Unbinding property with no fuel remaining? There is the case where a monk is an arahant whose fermentations have ended, who has reached fulfillment, finished the task, laid down the burden, attained the true goal, ended the fetter of becoming, and is released through right gnosis. For him, all that is sensed, being unrelished, will grow cold right here. This is termed the Unbinding property with no fuel remaining." (Note2)
Note1 and Note2 (commentary by Thanissaro Bhikkhu):
With fuel remaining (sa-upadisesa) and with no fuel remaining (anupadisesa): The analogy here is to a fire. In the first case, the flames are out, but the embers are still glowing. In the second, the fire is so thoroughly out that the embers have grown cold. The "fuel" here is the five aggregates. While the arahant is still alive, he/she still experiences the five aggregates, but they do not burn with the fires of passion, aversion, or delusion. When the arahant passes away, there is no longer any experience of aggregates here or anywhere else.