The rulings resulting from the one who abandons Ṣalāt (prayers) being an apostate include:

1. He loses his authority. This means that that he will not be authorised to do anything prescribed in Islam. Therefore, he will not have authority over minors or others, nor can he give any of his daughters or anybody else away in marriage. [Sheikh Al ‘Uthaymīn, Ḥukm Tārik Al-Ṣalāt (Rulings regarding those who abandon prayer), p.22]
2. He does not inherit from his relatives, because a disbeliever does not inherit from a Muslim and a Muslim does not inherit from a disbeliever. The evidence for this is the ḥadīth (narration) of Usāmah Bin Zayd in which the Prophet (May Allāh praise him and Peace be upon him) said, “A Muslim does not inherit from a disbeliever; nor does a disbeliever inherit from a Muslim.” [Reported by Bukhārī (6764)]
3. He is prohibited from entering Mecca and Al Masjid Al Ḥarām (the Grand Mosque). The evidence for this is that Allāh, Exalted is He, says “O you who have believed, indeed the polytheists are unclean, so let them not approach Al Masjid Al Ḥarām after this, their [final] year” [Sūrat Al Tawbah, Āyah no. 28]. [Sheikh Al ‘Uthaymīn, Ḥukm Tārik Al-Ṣalāt (Rulings regarding those who abandon prayer), p.23]
4. Any livestock that he is slaughtered is ḥarām (prohibited) whether that be a camel, cow, sheep or anything else that has to be slaughtered in order for it to be ḥalāl (permissible). This is because one of the conditions is that the person who slaughters the animal must be Muslim or a person of the Book (a Jew or a Christian). Anything slaughtered by an apostate, and idol worshipper, a fire worshipper, etc. is not ḥalāl (permissible). [Sheikh Al ‘Uthaymīn, Ḥukm Tārik Al-Ṣalāt (Rulings regarding those who abandon prayer), p.23]
5. It is not permissible to pray al janāzah (the funeral prayer) for him when he dies, or to perform du`ā’ (supplication) for him to be forgiven, because Allāh, exalted is He, says, “And do not pray [the funeral prayer, O Muhammad], over any of them who has died - ever - or stand at his grave. Indeed, they disbelieved in Allāh and His Messenger and died while they were defiantly disobedient” [Sūrat Al Tawbah, Āyah no. 84].
6. He is forbidden from marrying a Muslim woman because he is a disbeliever and disbelievers are not allowed to marry Muslim women. The evidence for this is that Allāh, exalted is He, says, “O you who have believed, when the believing women come to you as emigrants, examine them. Allāh is most knowing as to their faith. And if you know them to be believers, then do not return them to the disbelievers; they are not lawful [wives] for them, nor are they lawful [husbands] for them.” [Sūrat Al Mumtaḥanah, Āyah No. 10]. [Sheikh Al ‘Uthaymīn, Ḥukm Tārik Al-Ṣalāt (Rulings regarding those who abandon prayer), p.25]