I think this wins the thread. I wonder who would populate all those islands if the Austronesians didn't.
Papuan languages would expand west into more of OTL Indonesia, which they did to an extent in OTL anyway (Timor and other Papuan languages were a relatively recent expansion). Likewise Papuan languages would remain more prevalent in the Solomons than they were in OTL. There would probably be some expansion into parts of the Western Pacific (New Caledonia, Fiji etc), although much of Oceania would remain uninhabited by humans for a very long time.Who do you think fills the gap in Oceania? Austroasiatic? Papuan? Something stranger like Dravidian or Japonic?
More expansion of the Kra-Dai languages into Malaysia and western Indonesian languages is also likely. The Austroasiatic languages were in the process of being of displaced by Kra-Dai and other language families anyway, so its unlikely they would last in Indonesia even if they make it there.
Madagascar would probably be settled by speakers of Bantu languages (well, more so than in OTL).