As for Buddhism whether Susima's attitude is positively disposed or otherwise would continue to grow infact one of Asoka's wife was a Buddhist , although without Ashoka's patronage it would not be as popular as in our time line. I would see it becoming popular amongst the masses, albeit gradually taking a few centuries. The attitude of the authorities would be indifferent and there wont be any mass repression. But the specific details of rituals etc would be different given the fact the most probably the faith would not receive the huge booster shot with Ashoka's conversion and thus would grow differently, the effort of Asoka to canonize certain aspects of the Buddhist faith cannot be ignored and it was on the basis of this the orthodox Buddhist creed began to emerge. Without this the faith would grow organically and in time would become very popular and in a few centuries Kings and emperor would patronize it anyway. Perhaps it would evolve taking more of local faith and culture becoming more grass roots gradually merging with Vedic Hinduism or not, its hard to tell.
Going off tangent The role of Pushyamitra Shunga in persecution of Buddhists is disputed by modern scholarship, while it is true that he did cut of tax privilege's to the Sangha and the system of state sponsorship was curtailed it seems hard to believe that he engaged in any systematic persecutions of Buddhists , persecutions if any was sporadic and limited to a few places and the accounts of persecutions were written few decades after the death of Pushyamitra Shunga.
As for the survival of the Mauryan Dynasty, well it was a dammed to failure from the beginning. I would call it a failed political experiment. Prior to the rise of Nanda dynasty, the subcontinent was ruled by Mahajanapadas, these two Magadhan dynasty swept away centuries old way of governance, which strangely was popular with the ordinary masses and obviously, the elite , to be replaced by a autocratic and very unpopular system of government. The Mahajanapadas were yes small but their growth was organic, based on the needs of the local elites and they had a governing legacy spanning more than 800 years. These Magadhan Empires were probably trying to recreate a Persian Empire on the subcontinent, the Achaemenids did conqueror the Indus valley and swat valley where the greatest centers of learning was located , I am talking of Taxashila which is where the political architect of Mauryan Dynasty was located, Chanakya. It was also said that Chandragupta Mauryan used Persian, Sogdian, Bactrian Mercenaries to overthrow the Nanda Dynasty, these were the remnants of the Achaemenid troops, which is plausible since that empire ended a few years ago. My point is the empires were unprecedented in history and consequently it lacked any legitimacy. Its despotic rule made the situation worse. People tolerated the situation for years but when the going got tough like few bad harvests and the Greco Bactrian invasion, the empire fell like a pack of cards. Frankly the maurayas did a great disservice to india, they derailed the organic development of unity and replaced it with a system of autocracy.