The people of Paradise will abide therein for ever
Question

When the people of Paradise enter Paradise, for how long will they remain there? Will there come a time when they will leave Paradise?.
Praise be to Allah.When the people of Paradise enter Paradise, they will abide therein forever and never leave it. Similarly the people of Hell will abide therein forever and never leave it. 
It says in Fatawa al-Lajnah al-Daa’imah: 
With regard to Paradise, it is the abode of reward on the Day of Resurrection for those who believed and did righteous deeds. In it there are whatever delights people could desire. In it there is what no eye has seen, no ear has heard, nor has it ever entered the mind of man. Those who enter it will enjoy real pleasures in both a physical and a spiritual sense, and they will live there forever. It will never cease to exist and they will never leave, and their joy will never come to an end, and they will have nothing to disturb their joy. This is according to the definitive texts and the consensus of the scholars and believers. Allah says (interpretation of the meaning): 
“The description of the Paradise which the Muttaqoon (the pious) have been promised: Underneath it rivers flow, its provision is eternal and so is its shade; this is the end (final destination) of the Muttaqoon (the pious), and the end (final destination) of the disbelievers is Fire [Al-Ra’d 13:35] 
“Truly, the Muttaqoon (the pious) will be amidst Gardens and water-springs (Paradise).
(It will be said to them): ‘Enter therein (Paradise), in peace and security.’
And We shall remove from their breasts any deep feeling of bitterness (that they may have). (So they will be like) brothers facing each other on thrones.
No sense of fatigue shall touch them, nor shall they (ever) be asked to leave it” [Al-Hijr 15:45-47]
“This is a Reminder. And verily, for the Muttaqoon (the pious) is a good final return (Paradise), —
‘Adn (Eden) Paradise (everlasting Gardens), whose doors will be opened for them.
Therein they will recline; therein they will call for fruits in abundance and drinks;
And beside them will be Qaasiraat-at-Tarf [chaste females (wives) restraining their glances (desiring none except their husbands)], (and) of equal ages.
This it is what you (Al-Muttaqoon — the pious) are promised for the Day of Reckoning!
(It will be said to them)! Verily, this is Our provision which will never finish” [Saad 38:49-54] 
“Friends on that Day will be foes one to another except Al-Muttaqoon (the pious).
(It will be said to the true believers of Islamic Monotheism): My worshippers! No fear shall be on you this Day, nor shall you grieve,
(You) who believed in Our Ayaat (proofs, verses, lessons, signs, revelations, etc.) and were Muslims (i.e. who submit totally to Allah’s Will, and believe in the Oneness of Allah — Islamic Monotheism).
Enter Paradise, you and your wives, in happiness.
Trays of gold and cups will be passed round them; (there will be) therein all that inner-selves could desire, and all that eyes could delight in and you will abide therein forever.
This is the Paradise which you have been made to inherit because of your deeds which you used to do (in the life of the world).
Therein for you will be fruits in plenty, of which you will eat (as you desire)” [Al-Zukhruf 43:67-73]
And it is proven in the Sunnah that the Prophet (peace and blessings of Allah be upon him) said: “A caller will call out – i.e., to the people of Paradise – ‘You will be healthy and never fall sick; you will live and never die; you will stay young and never grow old; you will feel joy and never feel sorrow.’” Narrated by Muslim. 
It was also proven that the Prophet (peace and blessings of Allah be upon him) said: “Death will be brought, in the form of a black and white ram, on the Day of Resurrection. Then the command will be given to slaughter it, then it will be said: ‘O people of Paradise, it is eternal and there is no death! O people of Hell, it is eternal and there is no death!’” Narrated by Muslim in his Saheeh. 
Allah has confirmed that both Paradise and Hell are eternal and will last forever, and that the believers will abide in Paradise forever and the disbelievers will abide in Hell forever, in many verses of the Quran. And the proven Sunnah from the Prophet (peace and blessings of Allah be upon him) provides many details which leave no room for any doubt that this is true, and there is no room for misinterpretation of the clear texts. Whoever doubts this fact or misinterprets the clear texts is following his own whims and desires and displacing words from their right places [cf. al-Nisa’ 4:46], so he is one of the kaafirs.