Praise be to Allah, and peace and blessings be upon the Messenger of Allah.
Death is a reality that Allah has decreed for all His creation. Allah, the Exalted, says:
﴿كُلُّ نَفْسٍ ذَائِقَةُ الْمَوْتِ ثُمَّ إِلَيْنَا تُرْجَعُونَ﴾ [العنكبوت: 57]
“Every soul will taste death, then to Us you will be returned.” [Al-‘Ankabut: 57]
Allah, the Exalted, has informed us that when death comes to a person, he wishes to return to this world so that he may perform righteous deeds. However, this return will not happen. Allah says:
﴿حَتَّىٰ إِذَا جَاءَ أَحَدَهُمُ الْمَوْتُ قَالَ رَبِّ ارْجِعُونِ لَعَلِّي أَعْمَلُ صَالِحًا فِيمَا تَرَكْتُ ۚ كَلَّا ۚ إِنَّهَا كَلِمَةٌ هُوَ قَائِلُهَا ۖ وَمِن وَرَائِهِم بَرْزَخٌ إِلَىٰ يَوْمِ يُبْعَثُونَ﴾ [المؤمنون: 99-100]
“Until, when death comes to one of them, he says, ‘My Lord, send me back, that I may do righteousness in what I left behind.’ Never! It is only a word he is saying, and behind them is a barrier until the Day they are resurrected.” [Al-Mu’minun: 99–100]
It is authentically reported from the Prophet ﷺ that a martyr wishes to return to this world because of what he sees of Allah’s honor bestowed upon him. He wishes to return so that he may be killed in the cause of Allah once again. But Allah informs him that returning to this world is not possible.
Accordingly, it is not permissible to supplicate for the deceased to return to this world, or to ask Allah to bring him back to life after his death so that he may return to this world, because Allah has placed a barrier between death and resurrection. Return will only take place on the Day of Resurrection.
As for grieving over the deceased and longing for them, this is natural. What is prescribed is to supplicate for them to receive mercy, forgiveness, and elevated ranks, and to ask Allah to reunite you with them in Paradise.
And Allah knows best.