Some of those specific events could be interesting. There are legends that the small Malay-influenced states of western Papua were founded by people with great spiritual knowledge, and they brought with them Hindu relics. I don't see why Buddhism couldn't do the same, it's just said state would have to evolve in a very particular way and Buddhism would need to propagated among its people (easier said than done given the prevalence of "folk Buddhism" and syncretic beliefs in all Buddhist countries) for it to survive.Sorry, that was notes from my own planned Papuan TL leaking into that post, which has a reason in that TL but would probably not happen unless a series of very specific events occurred.
There apparently is to this day a very isolated area on the island of Lombok in Indonesia where folk Buddhist traditions persist, so it's definitely possible, the question is how widespread it would be. I think the highlands of Papua would be very poorly integrated with the coast--they're very hostile to outsiders after all, and generally don't have a lot of good resources--so it likely wouldn't be there.
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