I don't think Japan would be forced from Korea. The WAllies probably wouldn't care if they lose Manchuria, but I have a feeling that they would draw a line at Korea.
Now even having said that, I think the WAllies would still provide masses of equipment to Japan help them in Manchuria and might even consider using B-29s in air strikes against targets in the Soviet Union and China. I do however think that the WAllies would pour manpower into stopping Chinese expansion at the Yalu.
True, it might also see the first deployment of western troops in the Far Eastern Front, the Wallies previously content to let the Japanese fight for them while giving the Japanese what they need to stand up against the Chinese and the Soviets.
Now, if you'll excuse me, I'm having fantasies of a combined fleet of the Nagatos, Yamatos, North Carolinas, SoDaks and Iowas shelling the hell out of Chinese positions along the coast and defending Hong Kong.
I think this would depend if the Wallies are willing to escalate the war in the Far East, i.e. China has so far refrained from attacking into SE Asia, staying on the defensive against Japanese troops operating from Indochina. They might reinforce Hong Kong, but I'm not sure they start shelling coastal targets unless they really want to escalate, which could prove really problematic in the long-term. They might, strictly on military targets, if the Japanese are pushed back to the Yalu and the Chinese and the Soviets are gunning for the peninsula. Jiang may throw in the towel at this point, I'm not really sure. Victory in Manchuria, plus the Soviet juggernaut poised to strike into Western Europe and to continue the war in Iran...Jiang and Stalin may think the Allied position could be pushed to an extent.