In The Name of Allaah, The Most Merciful, The Bestower of Mercy.

Allaah [The Most High] said:

حُنَفَآءَ لِلَّهِ غَيۡرَ مُشۡرِكِينَ بِهِۦ‌ۚ وَمَن يُشۡرِكۡ بِٱللَّهِ فَكَأَنَّمَا خَرَّ مِنَ ٱلسَّمَآءِ فَتَخۡطَفُهُ ٱلطَّيۡرُ أَوۡ تَهۡوِى بِهِ ٱلرِّيحُ فِى مَكَانٍ۬ سَحِيقٍ۬

Hunafaa’ Lillaah [i.e. worship none but Allaah], not associating partners [in worship, etc.] with Him; and whoever associates partners to Allaah, it is as if he had fallen from the sky, and the birds had snatched him, or the wind had thrown him to a far-off place. [Surah Al-Hajj. Aayah 31]

[حُنَفَآءَ لِلَّهِ  ]- Meaning: turn to Allaah [in complete submission], worship Allaah alone and turn away from other than that. [غَيۡرَ مُشۡرِكِينَ بِهِۦ‌ۚ  – not associating partners (in worship, etc.) with Him]; [وَمَن يُشۡرِكۡ بِٱللَّهِ – and whoever associates partners to Allaah], then [فَكَأَنَّمَا خَرَّ مِنَ ٱلسَّمَآءِ فَتَخۡطَفُهُ ٱلطَّيۡرُ أَوۡ تَهۡوِى بِهِ ٱلرِّيحُ فِى مَكَانٍ۬ سَحِيقٍ۬    – it is as if he had fallen from the sky, and the birds had snatched him, or the wind had thrown him to a far off place].

This is the situation of the Mushrik, because Eemaan is like the sky- protected and raised high, so whoever abandons Eemaan he is like one who has fallen from the sky and is exposed to evil consequences and disasters- snatched by birds that will rip his limbs. Likewise, when the Mushrik abandons the protection of Eemaan, the devils snatch him from every direction and rip him apart, ruining both his religion and worldly life [i.e. because this worldly life is a place to perform righteous deeds for entry into paradise]. [Ref 1]

Allaah made it known in this Aayah that indeed the one who associates partners with Allaah and dies without repenting, then indeed he has fallen into destruction – neither has a way out of it nor can he be saved. He resembles someone who falls from the sky and lands on the earth and thus all his body is rip apart, the birds snatch them away and the wind throws them to a far-off place due to intense [manner in which the] wind blew his ripped body parts. So, whoever is described as one in such a situation, then indeed neither can he hope for a way out nor can he desire safety; rather he is definitely destroyed, because what normally happens is that the one who falls from the sky and lands on the earth, he does not reach the earth except that his body parts are ripped apart. And [if] the birds snatch his body parts and disperse with them, or the wind throws him to a far-away place, then this is an inevitable destruction and there is no way of avoiding it.

And that which is established in this noble Aayah – regarding the fact that the one who associates partners with Allaah is destroyed – has also been mentioned clearly in another place in the Qur’aan, such as the statement of Allaah: [إِنَّهُ ۥ مَن يُشۡرِكۡ بِٱللَّهِ فَقَدۡ حَرَّمَ ٱللَّهُ عَلَيۡهِ ٱلۡجَنَّةَ وَمَأۡوَٮٰهُ ٱلنَّارُ‌ۖ – Verily, whosoever sets up partners in worship with Allah, then Allah has forbidden Paradise for him, and the Fire will be his abode]. [Surah Al-Maa’idah. Aayah 72]

Allaah said:

إِنَّ ٱللَّهَ لَا يَغۡفِرُ أَن يُشۡرَكَ بِهِ

Verily, Allah forgives not that partners should be set up with him in worship. [Surah An-Nisaa Aayah 48]

And indeed there are other Aayaat [showing] that this inescapable destruction is related to the one who dies upon shirk and did not repent.

As for the one who repents before death, then indeed Allaah forgives Him because Islaam [i.e. submission to Allaah with Tawheed] wipes away that which was before it [i.e. shirk]. There are a number of Aayaat that indicate to this, such as the statement of Allaah: [قُل لِّلَّذِينَ ڪَفَرُوٓاْ إِن يَنتَهُواْ يُغۡفَرۡ لَهُم مَّا قَدۡ سَلَفَ – Say to those who have disbelieved, if they cease (from disbelief) their past will be forgiven]. [Surah Al-Anfaal. Aayah 38]

And those who invoke not any other ilah (god) along with Allah, nor kill such life as Allah has forbidden, except for just cause, nor commit illegal sexual intercourse and whoever does this shall receive the punishment. The torment will be doubled to him on the Day of Resurrection, and he will abide therein in disgrace; Except those who repent and believe (in Islamic Monotheism), and do righteous deeds, for those, Allah will change their sins into good deeds..[Surah Al-Furqaan. Aayaat 68-70]

Allaah said: [وَإِنِّى لَغَفَّارٌ۬ لِّمَن تَابَ وَءَامَنَ وَعَمِلَ صَـٰلِحً۬ا – And verily, I am indeed Forgiving to him who repents, believes (in My Oneness, and associates none in worship with Me) and does righteous good deeds]. [Surah Taahaa. Aayah 82]

However, if one’s repentance is at the time of death [i.e. when the soul reaches the throat], it will not benefit him. [Ref 2]

[Ref 1. An Excerpt from ‘Tafsir As-Sadi’. Slightly paraphrased]; [Ref 2: An Excerpt from ‘Adwaa Al-Bayaan. Tafseer Surah Al-Hajj. Aayah 31. Slightly paraphrased]

Read More Here Regarding Types of Shirk

Ahmad an-Najmee’s Kitaab at-Tawheed Chapter 3: Fear of Falling into Shirk