Macarthur was ordered to leave Corregidor and proceed to Australia. He used PT boats to break the Japanese blockade. He bounced back from his defeat in Bataan and went on to lead part of the US campaign in the PTO.
Now the question: what if Macarthur's PT boats were sunk and his escape failed?
Who would be the next general likely to replace a person such as Mac?
And how would this commander conduct his part of the Pacific campaign?
Mac's experience in Buna led him to accept the island-hopping strategy.
Without Mac, what could have been used instead?
Personally, I feel the loss of such a forceful personality would catapult the US Navy to the forefront of Pacific Theater operations. What I have in mind would be that most operations would be dictated by the Navy, i.e., the Navy would outline its operational needs to defeat Japan and the other services would follow suit to meet the strategic requirements. Army or Marine officers would still be used to command local campaigns but the overall strategic concept would be naval in nature.

In the ETO, I think it was the reverse.
If the Navy had lead without Mac, I personally think that Guadalcanal might not have been pushed through. Buna would still have happened, though.
I think fewer islands would have been attacked and the islands targeted would be converted to bases to support the Navy's logistical needs. The emphasis would be like Germany's U-boat campaign, and such a strategy could lead to fewer casualties and probably, a swifter strangulation and earlier isolation of much of Japan's defensive perimeter. Such a strategy would probably lead to the use of a better type of submarine and maybe improved wolf pack tactics. Japan is highly vulnerable to this because their navy didn't really have an efficient convoy system.
With Japan's outlying forces denied supplies, the US would be in a better position to choose where to strike next, leading to maybe a faster campaign. Large concentrations of Japanese forces would be left impotent and they would just wither on the vine without adequate supplies.
I know the priority was Europe first but I think the above might be a good compromise.
Mac had a tendency to go for the dramatic because of his ego. Without Mac, the US would've bypassed the Philippines. As for the commander I have in mind, Nimitz is the first in my mind. Is there another US officer that could step up aside from Nimitz?