Well, here's one of my ideas:
Rebellious Cham political leaders and their followers were sentenced of permanent banishment instead of execution: their destination, as they found out,was in a region composed of OTL Metro Manila, Bulacan and Cavite. There, like the earlier Cham settlers who were mostly tradersm they intermarried with the locals and raised families. The most curious aspect of this migration was their language was influenced by Austronesian focus and other linguistic features common to most Philippine languages. Besides, the Philippine Chams, as now they were called, settled in OTL eastern Iloilo, Guimaras and central to south Negros Occidental, influencing both the political and economic landscape of pre-Hispanic Visayas.