Buddhism and Hinduism would likely remai prevalent, though Christianity or Judaism or Zoroastrianism all could have the chance to take Islam's role.
IOTL Malaya and Indonesia became Muslim as a result of the traders and merchants sailing from Arabia, Persia and India being Muslims, which created an economic incentive for conversion and later missionaries and other groups moved in, so if you get traders and merchants from the same areas ITTL they could bring along whatever religions they belong to; in the case of Perisa that would be Zoroastrianism and in the case of Arabia that would be Christianity and Judaism*.
That all said I think you'd most likely though end-up with a more religiously pluralistic region, with Buddhism, Hinduism (both strengthened from Indian contacts), Chrsitianity, Judaism, Zoroastrianism and possibly even some of the Indigenous faiths from elsewhere all being introduced to the region and gaining converts/followers.
*Before the advent of Islam the Arabian peninsula, ranging from Jordan to Oman was split between Jews, Christians and followers of the Indigenous Arabian religions, one of which was a Monotheistic religion basd on a Lunar Goddess.