After Nibbana, can one be reborn again in Samsara? 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.