Death for the believer is a blessing and happiness, as it is the start of reward and happy everlasting life, and for the disbeliever is a start of punishment. The believers are transferred when they die from the this life which has difficulties and pain and sufferings, to the life of peace, pleasure and happiness.
Imam Hasan al-Mujtaba was asked about death, he replied: Death is the happiest day for the believer, and the hardest day for the hypocrite.
In Ziyarat Ameen Allah which is recommended to be recited in visiting every Imam, we read a great Du'a which includes: O Allah, make me always longing for the happiness of meeting your mercy (death) مشتاقة إلى فرحة لقائك
Real believer seeks from Allah (SWT) to grant him martyrdom because it is the best way to die then live everlasting happy life, and even those who do not die in war, their readiness to be martyr and longing for martyrdom , makes them get the degree of the martyrs.
The Prophetic Hadeeth says: Surely, any believer dies loving The Progeny of the Prophet, will die as Shaheed.
Loving Allah ( SWT) and serving his servants ( especially the children ) will make death a really happy day for the family.