When someone goes, they go only when they’re meant to go. They have already served their purpose here on earth, even though we will not always be entirely sure what that purpose is at the time of passing. God needs them up with him more than we do now.
Rest assured, those who pass never completely leave this earth. They will continue living on in spirit through the hearts they have touched and those who they had great impact upon on while alive, also in a more physical sense though the blood of their offspring and future kin.
Let us also not forget their is never an end to their works as angels.