This is a really interesting topic and given I’ve just returned from a holiday in Indonesia I wish I had something more to add but AngelDeJesus seems to have said all that I could argue. Maybe a more settled and agrarian Sulawesi, influenced by Majapahit or Srivijaya might remain Buddhist or Hindu?
It's interesting that the Cholas apparently didn't observe that taboo when they used their navy to invade Sri Vijaya. If Sri Vijaya was able to withstand the invasion, what would have been the subsequent relationship between Sri Vijaya and the Cholas or other Indian states. Just wondering if it would be more amicable such as an alliance or at least neutrality or more contentious like the Cholas treat Sri Vijaya as their "backyard" or as rivals to colonize other parts of the Indian Ocean e.g. Australia or East Africa.
The
kāla pāni taboo has been proven to be a small tradition amongst post-17th century North Indian elites that was blown into a full-fledged myth by British historians. Even before the Chola Empire’s invasions of Sri Vijaya there were plenty of fleeing Indian princelings who used to flee to Southeast-Asia alongside their retinues and marry into local elites to give them legitimacy.
Also archaeological digs have found prior to the Pandyas and Cholas slowly trying to gain influence in the Indonesian archipelago, a near millennium and a half before sailors from the Kalinga mahajanapada (modern day Orissa) were the ones who initiated the Indianisation of the region when Sadhába traders began to sail out to these places. The Hathigumpha inscriptions alongside large amounts of Mahameghavana coinage found in Kedah suggest that the area was under King Kharavela’s direct control c. 1st century BCE.
So much so that Rajendra Chola I conquered the region explicitly to for the great ports it housed to stage naval expeditions into the Bay of Bengal and beyond.