Answer:
I'll try my best
Explanation:
MacArthur was a one trick pony: Amphibious assaults. He would overwhelm coastal / island garrisons with Battle Ship delivered fire power, and inundate the island with American Soldiers and naval airpower into submission. He played his one trick in Korean War at Incheon. However, he has never conducted a successful high intensity land campaign. He did not partake in Okinawa, and failed to stop a combined arms assault on Luzon, as well as in Korea. In fact, his recommendation in the winter of 1950 was to evacuate Korea and reattempt an amphibious landing. US and Korea were lucky that he was fired at that point, and Ridgeway who cut his teeth in Europe brought the Chinese offensive to a halt in early 1951 at Chipyong Ni.
So, any counterfactual involving MacArthur staying onboard, would involve him expanding the war into China by assault landing Taiwanese (ROC) troops into Fujian, and perhaps into Yungui region, to try to link back up with RoC remnants on the Yunnan-Burma border. US Troops would have been landed alongside RoC forces into Shanghai - Nanjing region, replicating the successful Japanese amphibious landings there a decade earlier.
RoK forces and USMC would have reeneacted Incheon landing, perhaps coupled with a simultaneous landing at Wonsan, effectively double enveloping the PVA in southern Korea.
Will it have succeeded? PRC and NorKo had no real Navy at the time, and US enjoyed uncontested Air Supremacy. Only impediments to sea lane logistics would have been the Typhoons, and other natural disasaters.
MacArthur also wanted to remilitarize Japan and to use its veterans in this expended war effort. Most likely, his splintered efforts on multiple fronts would have been contained and eliminated in detail by the sheer mass of trained reserves that PLA had in early 1950s. However, if he did somehow succeed in expanding the beachheads and eventually connecting them, the area contorlled by US and proxy forces would have closely resembled the final disposition of troops by IJA in the summer of 1945, minus Manchuria. China will have been forced to recall the PVA to bolster the defense of Manchurian and Hebei. Korea would have been united, possibly, but at this point, there would have been a strong likelihood of Russia entering the war to defend Manchuria, and retake Korea… and perhaps a European Front opening, beginning with an overrunning of Berlin.
All in all, Truman made the right decision to remove this overrated one trick pony whose time had come.
