Did anyone get to God or Sach Khand before Guru Nanak?

Sikhs believe that the Almighty Himself sent his Guru form, the True Guru, Guru Nanak Dev Ji to save the world. As mentioned early, in essence Guru Nanak Dev Ji was no human, but the Divine Infinite Wisdom, and therefore existed throughout time to save the Seeker of Truth from spiritual darkness of ignorance:

ਤੂ ਸਤਿਗੁਰੁ ਚਹੁ ਜੁਗੀ ਆਪਿ ਆਪੇ ਪਰਮੇਸਰੁ ॥
ਸੁਰਿ ਨਰ ਸਾਧਿਕ ਸਿਧ ਸਿਖ ਸੇਵੰਤ ਧੁਰਹ ਧੁਰੁ ॥
ਆਦਿ ਜੁਗਾਦਿ ਅਨਾਦਿ ਕਲਾ ਧਾਰੀ ਤ੍ਰਿਹੁ ਲੋਅਹ ॥
ਅਗਮ ਨਿਗਮ ਉਧਰਣ ਜਰਾ ਜੰਮਿਹਿ ਆਰੋਅਹ ॥
ਗੁਰ ਅਮਰਦਾਸਿ ਥਿਰੁ ਥਪਿਅਉ ਪਰਗਾਮੀ ਤਾਰਣ ਤਰਣ ॥
ਅਘ ਅੰਤਕ ਬਦੈ ਨ ਸਲ੍ਯ੍ਯ ਕਵਿ ਗੁਰ ਰਾਮਦਾਸ ਤੇਰੀ ਸਰਣ ॥੨॥੬੦॥
“You are the True Guru, throughout the four ages; You Yourself are the Transcendent Lord. The angelic beings, seekers, Sidhs and Sikhs have served You, since the very beginning of time. You are primal, from the very beginning, and throughout the ages; Your Power supports the three worlds.”
(Ang 1406)

True Guru, the Infinite Divine Wisdom, is one with God and there remains no difference between the two. It is like a drop of water in the ocean. There is only “One God”, and True Guru remains immersed in Him and shows the path to the seeker of Truth and helps on the spiritual journey.
The difference was that Gurmat Naam was only available to select Bhagats in the past through Divine-Grace and intense Bhagti (meditative devotion). Through their intense Bhagti and Divine-Grace they found the Guru in the form of the formless. The Guru’s Bani (Divine Word) and Shabad has existed in all four ages. The sound of Gurbani has existed throughout time in the air and space however only those few select great souls were able to access the Divine Guru and achieve liberation.

ਬਾਣੀ ਵਜੀ ਚਹੁ ਜੁਗੀ ਸਚੋ ਸਚੁ ਸੁਣਾਇ ॥
“The Word of the Guru’s Bani vibrates throughout the four ages. As Truth, it teaches Truth.”
(Ang 35)

Now, in Kaljug (present era of time), Guru Nanak Dev Ji came and offered Naam openly to humanity and that is why Kaljug is in fact the best of the Jugs (eras of time):

ਆਸਾ ਮਹਲਾ ੫ ॥
ਅਗਮ ਅਗੋਚਰੁ ਦਰਸੁ ਤੇਰਾ ਸੋ ਪਾਏ ਜਿਸੁ ਮਸਤਕਿ ਭਾਗੁ ॥
ਆਪਿ ਕ੍ਰਿਪਾਲਿ ਕ੍ਰਿਪਾ ਪ੍ਰਭਿ ਧਾਰੀ ਸਤਿਗੁਰਿ ਬਖਸਿਆ ਹਰਿ ਨਾਮੁ ॥੧॥
ਕਲਿਜੁਗੁ ਉਧਾਰਿਆ ਗੁਰਦੇਵ ॥
ਮਲ ਮੂਤ ਮੂੜ ਜਿ ਮੁਘਦ ਹੋਤੇ ਸਭਿ ਲਗੇ ਤੇਰੀ ਸੇਵ ॥੧॥ ਰਹਾਉ ॥
ਤੂ ਆਪਿ ਕਰਤਾ ਸਭ ਸ੍ਰਿਸਟਿ ਧਰਤਾ ਸਭ ਮਹਿ ਰਹਿਆ ਸਮਾਇ ॥
ਧਰਮ ਰਾਜਾ ਬਿਸਮਾਦੁ ਹੋਆ ਸਭ ਪਈ ਪੈਰੀ ਆਇ ॥੨॥
ਸਤਜੁਗੁ ਤ੍ਰੇਤਾ ਦੁਆਪਰੁ ਭਣੀਐ ਕਲਿਜੁਗੁ ਊਤਮੋ ਜੁਗਾ ਮਾਹਿ ॥
ਅਹਿ ਕਰੁ ਕਰੇ ਸੁ ਅਹਿ ਕਰੁ ਪਾਏ ਕੋਈ ਨ ਪਕੜੀਐ ਕਿਸੈ ਥਾਇ ॥੩॥
ਹਰਿ ਜੀਉ ਸੋਈ ਕਰਹਿ ਜਿ ਭਗਤ ਤੇਰੇ ਜਾਚਹਿ ਏਹੁ ਤੇਰਾ ਬਿਰਦੁ ॥
ਕਰ ਜੋੜਿ ਨਾਨਕ ਦਾਨੁ ਮਾਗੈ ਅਪਣਿਆ ਸੰਤਾ ਦੇਹਿ ਹਰਿ ਦਰਸੁ ॥੪॥੫॥੧੪੦॥
“Aasaa, Fifth Mehl: The Blessed Vision of Your Darshan is unapproachable and incomprehensible; he alone obtains it, who has such good destiny recorded upon his forehead. The Merciful Lord Vaheguru has bestowed His Mercy, and the True Guru has granted the Lord’s Name. ||1|| The Divine Guru is the Saving Grace in this Dark Age of Kaljug. Even those fools and idiots, stained with faeces and urine, have all taken to Your service. ||1||Pause|| You Yourself are the Creator, who established the entire world. You are contained in all. The Righteous Judge of Dharma is wonder-struck, at the sight of everyone falling at Vaheguru’s Feet. ||2|| The Golden Age of Sat Yuga, the Silver Age of Trayta Yuga, and the Brass Age of Dwaapar Yuga are good; but the best is the Dark Age, the Iron Age, of Kaljug. As we act, so are the rewards we receive; no one can take the place of another. ||3|| O Dear Vaheguru, whatever Your devotees ask for, You do. This is Your Way, Your very nature. With my palms pressed together, O Nanak, I beg for this gift; Vaheguru, please bless Your Saints with Your Vision. ||4||5||140||”
(Ang 406)

Furthermore. Gurbani says:

ਸਤਿਗੁਰ ਕੀ ਜਿਸ ਨੋ ਮਤਿ ਆਵੈ ਸੋ ਸਤਿਗੁਰ ਮਾਹਿ ਸਮਾਨਾ ॥
ਇਹ ਬਾਣੀ ਜੋ ਜੀਅਹੁ ਜਾਣੈ ਤਿਸੁ ਅੰਤਰਿ ਰਵੈ ਹਰਿ ਨਾਮਾ ॥੧॥ ਰਹਾਉ ॥
ਚਹੁ ਜੁਗਾ ਕਾ ਹੁਣਿ ਨਿਬੇੜਾ ਨਰ ਮਨੁਖਾ ਨੋ ਏਕੁ ਨਿਧਾਨਾ ॥
ਜਤੁ ਸੰਜਮ ਤੀਰਥ ਓਨਾ ਜੁਗਾ ਕਾ ਧਰਮੁ ਹੈ ਕਲਿ ਮਹਿ ਕੀਰਤਿ ਹਰਿ ਨਾਮਾ ॥੨॥
“One who accepts the wisdom of the True Guru’s Teachings, is absorbed into the True Guru. The Lord’s Name abides deep within the nucleus of one who realizes the Baani of the Guru’s Word within their soul. ||1||Pause|| In the sanctuary of the Guru one understands that the essence of the teachings of the four ages: for the human race, the Name of the One Lord is the greatest treasure. (The Vedas and the other Hindu Scriptures etc have been saying that) celibacy, self-discipline and pilgrimages were the essence of Dharma in those past ages; but in this Dark Age of Kaljug, (Guru Nanak has come and said that) the Praise of the Lord’s Name is the essence of Dharma. ||2||”
(Ang 797)

No one is condemned to Hell simply for having incorrect belief. It is our actions, which are judged. A Sikh, who has meditated on Naam and lived the Path of Gurmat will break through this prison of action/reaction or Karma and enter Sachkhand. Not everyone is fortunate and has the good karma of meeting Satguru. However, through good Karma they have the opportunity of living Gurmat in a future life.
Other religions like Islam, Christianity and Judaism, cannot explain what happened to those countless Inuit and Natives and Aborigines and African Tribalists who did not have a concept of a single God as in the Abrahamic religions? Sadly, Islam and Semitic religions would condemn these people to Hell for worshiping many gods. Was it their fault that they had not heard of Islam, Christianity or heard of the God of Abraham that they should be eternally cast to Hell? This is pure injustice and blind discrimination. This is not reflective of an All-Loving and Just God, who has implemented Just and Fair Laws in the Universe.
Sikhism answers that it was not in their karma to know of God and depending on their actions they may be rewarded with human life again and the opportunity to know God. They are by no means condemned for having wrong belief. Condemnation is for those who commit wrong action. Those who meet the True Guru, embrace the True Guru and live the Path of Gurmat Naam are truly blessed and are fortunate.