> Why did he not divert the water first and ask for permission later?
IIRC according to some timelines, the uphill lahaina fire did not restart until around 3:00 PM. At about 3:30 PM, the local emergency management sends out a shelter-in-place message. At 4:45PM, they close the bypass. In particular, given all of the apparent simultaneous communications problems, they might have been faced with a no-win situation: if they OK’d the use of the water without permission and it worked, then the emergency would have ceased, and they would be open to a lawsuit for stealing culturally significant water resource for no evident bottom line reason. these kinds of problems could have been solved or at least ameliorated by a comprehensive fire emergency plan that covered wind and weather, emergency water usage, power distribution (including emergency power), ground foliage trimming, communication (including siren usage and cell phone coverage), and emergency evacuation. up through the present, i am not aware that such an emergency fire plan exists. it would not surprise me if such a plan was a rarity on other islands (outside of oahu perhaps).
How about if they had had pumps in the ocean and used that water instead to put the fires out?