What happens to the human in afterlife if he does not believe in any God or any theory related to god?
Do any Vedas mention anything regarding this?
What happens if anyone is not believing in God? What happens to the human in afterlife if he does not believe in any God and any theory related to god?
The answers of these questions are provided in Shreemad Bhagvat Gita by Shree Krishna. Here Shree Krishna is exactly telling Arjuna about this.
अश्रद्दधानाः पुरुषा धर्मस्यास्य परन्तप।
अप्राप्य मां निवर्तन्ते मृत्युसंसारवर्त्मनि।।9.3।।
aśraddadhānāḥ puruṣā dharmasyāsya paran-tapa aprāpya māṁ nivartante mṛtyu-saṁsāra-vartmani
Meaning - Those who are not faithful in this devotional service cannot attain Me, O conqueror of enemies. Therefore they return to the path of birth and death in this material world. BG 9.3
अज्ञश्चाश्रद्दधानश्च संशयात्मा विनश्यति।
नायं लोकोऽस्ति न परो न सुखं संशयात्मनः।।4.40।।
ajñaścāśraddadhānaśca saṅśayātmā vinaśyati. nāyaṅ lōkō.sti na parō na sukhaṅ saṅśayātmanaḥ ৷৷ 4.40 ৷৷
Meaning- One who is ignorant and faithless, and has a doubting mind perishes. Neither this world nor the next nor happiness exists for one who has a doubting mind. BG 4.40
श्रद्धावाँल्लभते ज्ञानं तत्परः संयतेन्द्रियः।
ज्ञानं लब्ध्वा परां शान्तिमचिरेणाधिगच्छति।।4.39।।
śraddhāvāḻ labhate jñānaṁ tat-paraḥ saṁyatendriyaḥ jñānaṁ labdhvā parāṁ śāntim acireṇādhigacchati
Meaning -A faithful man who is dedicated to transcendental knowledge and who subdues his senses is eligible to achieve such knowledge, and having achieved it he quickly attains the supreme spiritual peace. BG 4.39
tad-buddhayas tad-ātmānas tan-niṣṭhās tat-parāyaṇāḥ gacchanty apunar-āvṛttiṁ jñāna-nirdhūta-kalmaṣāḥ
Meaning - When one’s intelligence, mind, faith and refuge are all ﬁxed in the Supreme, then one becomes fully cleansed of misgivings through complete knowledge and thus proceeds straight on the path of liberation. BG 5.17
So from this conversation we come to know that people who are non believes or Atheist or who do not believe in God or any theories related ( Shastra) , do not get Supreme knowledge , Eternal peace in this as well as other worlds.They again get rebirth here on earth.So they do not attain Moksha or liberation, as told in various texts as final goal of Human being.
What happens to the human in afterlife if he does not believe in any God and any theory related to god? Does anything regarding this has mentioned in any Vedas?
Well,not sure about the Srutis(Vedas), but Smritis do talk a lot about the consequences of non-believers of Gods or Shastras(Srutis and Smritis) or the Atheists.
Atheism is condemned all through out Hindu Shastras.Some mention it as minor sin while others mention it as a grave one.
The Manu Smriti mentions it as a minor offence and also says that it leads to loss of caste.
Manu Smriti 4.163. Let him avoid atheism, cavilling at the Vedas, contempt of the gods, hatred, want of modesty, pride, anger, and harshness.
Manu 11.66. Stealing grain, base metals, or cattle, intercourse with women who drink spirituous liquor, slaying women, Sudras, Vaisyas, or Kshatriyas, and atheism, (are all) minor offences, causing loss of caste (Upapataka).
Now,even your question about what one becomes in afterlife as a consequence is answered in Scriptures.
Those who have committed a crime effecting loss of caste, enter the bodies of amphibious animal(Vishnu smriti ,XLIV,6)
So,atheism,contempt of God,reviling the Vedas all leads to loss of caste and loss of caste to rebirth as an amphibian.(HAHA)
In anycase,even if you believe in these "amphibian" things or not, like said in the answer above by SwiftPushkar,non-believers(of Gods and Shastras) will have to take birth after birth.
So,not recommended at all.Have faith and make your life blissful.:)