If Dara Shukoh had succeeded ShahJahan instead of Aurangazeb the Mughal Empire might have gone on for two three generations more, ie, for another century at the most. Any how it was going to collapse and would have collapsed in the nineteenth century.
Actually the Empire was dying after Aurangzeb and his son and grandson just kept it barely alive. Afterwards the corpse of the Empire was covered in royal clothes and held in a sitting position first by the Marathas and later by the East India Company till the formal declaration of death and burial in 1857. The Empire was practically dead several decades ago.
Aurangzeb under whom the Empire expanded to its maximum extent had also sowed the seeds for its eventual collapse. The formal period of the Mughal Empire can be dated from 1526(the Ist Battle of Panipat) to 1857(the ouster and exile of Bahadur Shah II). The actual period of its life was from 1556 to 1707, the death of Aurangzeb.