Is it permissible to grieve for a man who died as a disbeliever, because he will abide for ever in Hell?

No File Exists
Check below answers in case you are looking for other related questions:
Distressed After Plane Crash
How can she congratulate a non-Muslim girl who was in an illicit relationship with a boy and is going to marry him?

No File Exists
Related Answers:
Is it permissible for him to sell gifts that have to do with kaafir festivals?
Does Islam regard non-Muslims with mercy and compassion?
Why does Islam forbid Muslims to imitate disbelievers?
Distressed After Plane Crash
How can she congratulate a non-Muslim girl who was in an illicit relationship with a boy and is going to marry him?

Recommended answers for you:
Qaseedat al-Burdah by al-Busayri and an explanation of what it contains of kufr and heresy
The seven sins that doom a person to Hell
Al Sunnan Al Rawatib (Sunnah Prayers associated with Fardh Prayers)
If his wife does not agree to him being away for more than six months
She feels sad and depressed, and is asking for a solution