Answer in the Quran.
11:105 On the Day it comes, no person will speak except with His permission. Some of them will be distraught, some will be happy.
11:106 As for those who are distraught, they will be in the Fire; in it for them is a sighing and a wailing.
11:107 Abiding therein as long as the heavens and the earth exist, except for what your Lord wishes. Your Lord does as He pleases.
11:108 As for those who are happy, they will be in the Paradise; abiding therein as long as the heavens and the earth exist, except for what your Lord wishes, a giving without end.
According to my understanding Allah is Just and Merciful both are his attributes.
The Quran repeatedly comfort us by reminding us Allah’s perfect justice. The following verse provides us with a precise idea of Allah’s justice and mercy:
“For those who did good work there will be the best and more. . . As for those who earned evil, they will receive equivalent evil (10:27).
Suffering in an eternal Hell creates a contradiction between this divine justice of Allah, since eternity can not be equal to an evil committed in during a limited life span of a human. However, eternal punishment in life time of a non eternal Hell avoids such a contradiction.
After receiving an equivalent punishment the chief evil-doers like those referred in verse 4:48, will be eliminated from existence. They will end up in Hell and Hell will end up in nothingness.
If there is no reward and punishment committed by humans in this life which they will receive as in form of Hell and Paradise on judgment day than this will be against his attributes. So Allah can not be Unjust and Merciless. Astagfirullah
All the Promises made by Allah about Hell and Paradise in the Quran are not fake but REAL.