It is not permissible to uncover the face of the deceased after he has placed in the grave
Question

Once the deceased has been placed in the grave, is it permissible to uncover his face or should we leave it covered?.
Praise be to Allah.Shaykh Ibn Baz (may Allah hav mercy on him) said: 
It should not be uncovered, rather his entire body should be covered, unless he is a muhrim (in ihram for Hajj or ‘Umrah), in which case his face and head should be uncovered, because the Prophet (peace and blessings of Allah be upon him) said concerning a muhrim who died in ‘Arafah: “Do not cover his head, for he will be raised on the Day of Resurrection reciting the Talbiyah.” Agreed upon. According to a version narrated by Muslim: “Do not cover his head or his face, for he will be raised on the Day of Resurrection reciting the Talbiyah.” 
And he also said: 
It is not permissible to uncover the face of the deceased, whether a man or a woman, once he or she has been placed in the lahd (niche in the grave), rather it must be covered with the shroud, unless the deceased was in ihram, in which case neither the head nor the face should be covered. But if the deceased is a woman than her face should be covered with the shroud even if she was in ihram, because it is ‘awrah. 
Majallat al-Buhooth al-Islamiyyah (68/44).