In dictionaries Default is identified as: a situation or condition that obtains in the absence of active intervention. There are a lot of examples to this default in Islam:
1- A creator: since we did not prove that existence can come from not existence we have to believe there is a creator.
52:35 Have they themselves been created without anything [that might have caused their creation]? Or are they the creators?أَمْ خُلِقُوا مِنْ غَيْرِ شَيْءٍ أَمْ هُمُ الْخَالِقُونَ (52:35)
2- One creator: since the laws of cosmos do not contradict with one another or change over time there is no good evidence to support more than one creator.
21:22 If there were therein gods beside Allah, then verily both (the heavens and the earth) had been disordered. Glorified be Allah, the Lord of the Throne, from all that they ascribe (unto Him). لَوْ كَانَ فِيهِمَا آلِهَةٌ إِلَّا اللَّهُ لَفَسَدَتَا فَسُبْحَانَ اللَّهِ رَبِّ الْعَرْشِ عَمَّا يَصِفُونَ (21:22)
3- Prophethood: There is no proofs of the prophets were liars. They were few chosen from billions of peoples and they were proved to be honest and disproved to be liars. The default here is God prophets should be humans like us not angels, not birds, not trees.. They were not liars and they are the medium or the connection between God and us. They had miracles or prophecies to prove to people that they are sent by God.
19:58 These are they unto whom Allah showed favor from among the prophets, of the seed of Adam and of those whom We carried (in the ship) with Noah, and of the seed of Abraham and Israel, and from among those whom We guided and chose. When the revelations of the Beneficent were recited unto them, they fell down, adoring and weeping.
أُوْلَئِكَ الَّذِينَ أَنْعَمَ اللَّهُ عَلَيْهِم مِّنَ النَّبِيِّينَ مِن ذُرِّيَّةِ آدَمَ وَمِمَّنْ حَمَلْنَا مَعَ نُوحٍ وَمِن ذُرِّيَّةِ إِبْرَاهِيمَ وَإِسْرَائِيلَ وَمِمَّنْ هَدَيْنَا وَاجْتَبَيْنَا إِذَا تُتْلَى عَلَيْهِمْ آيَاتُ الرَّحْمَن خَرُّوا سُجَّدًا وَبُكِيًّا (19:58)
You have the choice to believe them now or in the day of judgment when it will be too late.
39:69 And the earth shineth with the light of her Lord, and the Book is set up, and the prophets and the witnesses are brought, and it is judged between them with truth, and they are not wronged.
وَأَشْرَقَتِ الْأَرْضُ بِنُورِ رَبِّهَا وَوُضِعَ الْكِتَابُ وَجِيءَ بِالنَّبِيِّينَ وَالشُّهَدَاء وَقُضِيَ بَيْنَهُم بِالْحَقِّ وَهُمْ لَا يُظْلَمُونَ (39:69)
4- Islam: since people had failed to prove lies against Muhammad (PBUH) and continue to fail to come up with a book like the Quran, Islam by default Islam is the truth. You are invited to disprove it, help yourself read the Quran but if you fail then you have to accept it, this is a default.
17:88 Say: Verily, though mankind and the jinn should assemble to produce the like of this Qur'an, they could not produce the like thereof though they were helpers one of another. - قُل لَّئِنِ اجْتَمَعَتِ الإِنسُ وَالْجِنُّ عَلَى أَن يَأْتُواْ بِمِثْلِ هَـذَا الْقُرْآنِ لاَ يَأْتُونَ بِمِثْلِهِ وَلَوْ كَانَ بَعْضُهُمْ لِبَعْضٍ ظَهِيرًا (17:88)
5- Spiritually: humans have the inborn desire to worship one God and to live with him and by him. This relationship even gets stronger than our relationship with our family members. The spiritual feeling and experience is too strong that is we can not disprove it and do not have the means even to disprove it, it is typically a default. If someone decided to astray from God with his mind and soul it does not prove to us that there is no human spirituality.
13:28 Who have believed and whose hearts have rest in the remembrance of Allah. Verily in the remembrance of Allah do hearts find restالَّذِينَ آمَنُواْ وَتَطْمَئِنُّ قُلُوبُهُم بِذِكْرِ اللّهِ أَلاَ بِذِكْرِ اللّهِ تَطْمَئِنُّ الْقُلُوبُ (13:28)
6- After life: According to Islam: Humans are by default entitled to inhabit at heaven if they would submit to God's messages. Active denial, arrogance and resisting are against the inner cry of their souls to find God and in their inheritance of God's spirit to be righteous. If you can not disprove there is no after life by default there is after life for a lot of people since many feel the existence of God and connect with him through visions including me.
7:27 O children of adam! Do not allow Satan to seduce you in the same way as he caused your ancestors to be driven out of the garden: he deprived them of their garment [of God-consciousness] in order to make them aware of their nakedness. Verily, he and his tribe are lying in wait for you where you cannot perceive them!  Verily, We have placed [all manner of] satanic forces near unto those who do not [truly] believe;
يَا بَنِي آدَمَ لاَ يَفْتِنَنَّكُمُ الشَّيْطَانُ كَمَا أَخْرَجَ أَبَوَيْكُم مِّنَ الْجَنَّةِ يَنزِعُ عَنْهُمَا لِبَاسَهُمَا لِيُرِيَهُمَا سَوْءَاتِهِمَا إِنَّهُ يَرَاكُمْ هُوَ وَقَبِيلُهُ مِنْ حَيْثُ لاَ تَرَوْنَهُمْ إِنَّا جَعَلْنَا الشَّيَاطِينَ أَوْلِيَاء لِلَّذِينَ لاَ يُؤْمِنُونَ (7:27)
7- God's wrath: is the default after he send his messengers. The wickedness of humans commonly preceded the coming of his messengers. This takes several forms like widespread denial of God or widespread injustices and corruptions. Same with the second coming of Jesus. Thus when God send warning before his wrath we have to respect that and work together to please him.
9:70 Have, then, the stories of those who preceded them never come within the ken of these [hypocrites and deniers of the truth]?-[the stories] of Noah's people, and of [the tribes of] `Ad and Thamud, and of Abraham's people, and of the folk of Madyan, and of the cities that were overthrown?  To [all of] them their apostles had come with all evidence of the truth. [but they rejected them:] and so it was not God who wronged them [by His punishment], but it was they who wronged themselves.
أَلَمْ يَأْتِهِمْ نَبَأُ الَّذِينَ مِن قَبْلِهِمْ قَوْمِ نُوحٍ وَعَادٍ وَثَمُودَ وَقَوْمِ إِبْرَاهِيمَ وِأَصْحَابِ مَدْيَنَ وَالْمُؤْتَفِكَاتِ أَتَتْهُمْ رُسُلُهُم بِالْبَيِّنَاتِ فَمَا كَانَ اللّهُ لِيَظْلِمَهُمْ وَلَـكِن كَانُواْ أَنفُسَهُمْ يَظْلِمُونَ (9:70)
8- The default at the day of judgment is no intercession to the disbelievers ( it is God compassion is the default that there will be intercession to the believers). It is not discrimination against them they did discriminate against their God and despite all his power and Glory and they denied him. They acknowledged a single flower and a small mouse and denied their creator or worshiped some of his creation. They worshiped a cow and other animals and denied him.
2:123 and remain conscious of [the coming of] a Day when no human being shall in the least avail another, nor shall ransom be accepted from any of them, nor shall intercession be of any use to them, and none shall be succoured.
وَاتَّقُواْ يَوْماً لاَّ تَجْزِي نَفْسٌ عَن نَّفْسٍ شَيْئاً وَلاَ يُقْبَلُ مِنْهَا عَدْلٌ وَلاَ تَنفَعُهَا شَفَاعَةٌ وَلاَ هُمْ يُنصَرُونَ (2:123)
19:87 [on that Day] none will have [the benefit of] intercession unless he has [in his lifetime] entered into a bond with the Most Gracious.
لَا يَمْلِكُونَ الشَّفَاعَةَ إِلَّا مَنِ اتَّخَذَ عِندَ الرَّحْمَنِ عَهْدًا (19:87)
9- Existence of Satan: by default since the evil that people do despite that the good pays more and the common good that is missing tell you loudly there is Satan. You do not have evidences to refute that he is real, he is a default particularly so if you do not follow God's message.
7:175 And tell them what happens to him to whom We vouchsafe Our messages and who then discards them: satan catches up with him, and he strays, like so many others, into grievous error.
وَاتْلُ عَلَيْهِمْ نَبَأَ الَّذِيَ آتَيْنَاهُ آيَاتِنَا فَانسَلَخَ مِنْهَا فَأَتْبَعَهُ الشَّيْطَانُ فَكَانَ مِنَ الْغَاوِينَ (7:175)