Best case scenario is that this enables the US to recognize the guerrilla operations on Mindanao much earlier, and eliminates the issues complicating unification of the guerrilla movement since their is a Major General in command, and MacArthur's Australian headquarters would recognize who Sharp is. However, I don't see William Sharp doing a better job than Wendell Fertig did, the real life leader of the Allied guerrilla war on Mindanao. Hopefully General Sharp leaves Mindanao as soon as possible and leaves a promoted Fertig in command.
Worse case scenario is that the non-surrendering of American units on Mindanao means the Japanese concentrate efforts there at the beginning and wipe out a lot of the initial guerrilla units as they hunt down the remaining American soldiers. However, it is possible that if they flee to the hills and disappear for a long time, the Japanese may just leave and declare victory.