The fall of Mauryan Empire was a great disaster for India and also Buddhism. But the unity and the strength of the empire depended too much on the personality of the emperor in those days. The establishment of the Mauryan Empire itself was an accomplishment of a genius like Chanakya and the prowess of Chandragupta Maurya. The Chandragupta had able successors like Bindusara and Ashoka. But the successors of Ashoka were not strong enough to carry on. If Kunala, the able son of Ashoka was not blinded as a result of a conspiracy, he might have made a successful emperor. The Maurya Empire failed to develop a self-sustaining bureaucracy as in China, able to carry on under weak rulers. All empires in India faced the same problem. The Guptas were successful under powerful emperors like Samudragupta, Vikramaditya or Kumaragupta. The Cholas were successful under emperors like Rajaraja or Rajendra. Mughals maintained their power when they had able emperors like Akbar, Jahangir or Shahjahan. All empires were based on the ability of certain individuals and collapsed when able rulers were not available.
The Buddhism disappeared from India due to various reasons. The growth of Buddhism was due to the growth of many superstitions and rituals like animal and even human sacrifices. The arrival of Buddhism and Jainism led to the stoppage of many of the bloody sacrifices. The rulers and the merchants had supported Buddhism and gave liberal contributions to the Sanghas. But as Hinduism adopted many of the features of Buddhism, especially non-violence and vegetarianism, Buddhism also adopted certain rituals and beliefs of Hinduism. Buddha himself was adopted as an avatar of Vishnu. In India, before the advent of Islam, the religions were not exclusive as in the Semitic world.It was similar to the East Asian system where one could follow different religious systems simultaneously. Thus Buddhism became indistinguishable from Hinduism and lost its identity. In fact Shaivism and Vaishnavism were like separate religions, often feuding along with Buddhism, Jainism and Shakteya traditions. In course of time every system came under the label of Hinduism.