the claim is only made by hindus, there is no reason to think that aurangzeb caused the demise of the mughals.
He executed Dara Shikoh (who might have actually strengthened the Mughal empire with his wise tolerant policies), Murad Baksh (his brother), Sulaiman Shikoh (his nephew and Dara Shikoh's eldest son), Sambhaji Maharaj (who was Shivaji Maharaj's son) and the influential Sikh guru Guru Tegh Bahadur. The inhuman executions of Guru Tegh Bahadur and Sambhaji Maharaj especially alienated the Sikhs and Marathas respectively.
Historian Will Durant writes:
"Aurangzeb cared nothing for art, destroyed its "heathen" monuments with coarse bigotry, and fought, through a reign of half a century, to eradicate from India almost all religions but his own. He issued orders to the provincial governors, and to his other subordinates, 'to raze to the ground all the temples of either Hindus or Christians, to smash every idol, and to close every Hindu school. In one year (1679–80) sixty-six temples were broken to pieces in Amber alone, sixtythree at Chitor, one hundred and twenty-three at Udaipur; and over the site of a Benares temple especially sacred to the Hindus he built, in deliberate insult, a Mohammedan mosque. He forbade all public worship of the Hindu faiths, and laid upon every unconverted Hindu a heavy capitation tax. As a result of his fanaticism, thousands of the temples which had represented or housed the art of India through a millennium were laid in ruins. We can never know, from looking at India today, what grandeur and beauty she once possessed. Aurangzeb converted a handful of timid Hindus to Islam, but he wrecked his dynasty and his country. A few Moslems worshiped him as a saint, but the mute and terrorized millions of India looked upon him as a monster, fled from his tax-gatherers, and prayed for his death. During his reign the Mogul empire in India reached its height, extending into the Deccan; but it was a power that had no foundation in the affection of the people, and was doomed to fall at the first hostile and vigorous touch. The Emperor himself, in his last years, began to realize that by the very narrowness of his piety he had destroyed the heritage of his fathers."
Also, the economy of the Mughal empire took a big hit when he came to the Deccan in 1681 with atleast 5 lakh of his camp followers.