Assuming that an ASB changes the minds of many in the IJA and there is a peace in China BEFORE PH, you see Japan still holding Manchuria, Korea, Formosa, and various Pacific Islands - more or less the Japanese Empire of 1935 or thereabouts. I expect Chiang will use the end of the war with Japan to crush the communists, which he can do in this scenario and assuming the USSR is busy fighting Germany 1941-45 they can't aid Mao even if they want to.
Since the impetus behind the Manhattan Project was using the bomb against Germany, this will continue. Depending in when Germany surrenders, you may get the project going to the first bomb tests - in any case atomic weapons will exist sometime in the 40s. Imperial Japan will work to get them once they are out, and will eventually become an independent atomic power, although well after the USA, USSR, Britain and (maybe) France.
If the war in China ends in fall, 1941 even with a non-aggression pact, the fact that Japan now has more military power to put along the Japan-Soviet border means some of the Siberian forces that went west will probably stay in the east. This may or may not have an effect on the war, not necessarily Germany wins or even takes Moscow, but perhaps the advance of Soviet forces west is a little slower and the cold war border further east/different than OTL. Certainly Southern Sakhalin/Karafuto and the Kurils will not be Soviet territory here, which does change the geopolitics there especially in the light of a continued strong IJN.
I expect that at some time after the end of WWII the US and other western powers will hold their nose and come to some sort of anti-communist agreement with Japan, although probably not a SEATO that includes Japan. Inclusion of Japan in any sort of defense pact, and US direct guarantees will be long in coming if at all. Look how long it took for Spain to get in to NATO as an example.
Any and all of this depends on Japan and China coming to some settlement BEFORE PH. Once Japan has attacked PH, and you have attacks on Guam, Wake, and the PI (with the Bataan Death March) the Japanese and Chinese ending that fight won't mean all is well between Japan and the USA.