Mao was very critical in making the key decisions that lead to victory. By 1941, Mao had essentially defeated Wang Ming and the Comintern faction of the CCP (which would take orders direct from Moscow instead of accepting Mao's lead), but the rectification campaigns of 1943 which molded the party in his image had not happened yet. So a lot depends on who assumes leadership of the CCP. When 1945 happens and everyone is pressing for the CCP and KMT to come to terms on a unified government, the new CCP leaders might actually try to make it work rather than attempt a military solution based on new bases in Manchuria which is what Mao pushed. You might also get new leaders who are actually interested in fighting the Japanese first which Mao did not want to do at all. Mao was constantly fending off attempts by the other Chinese Communists to fight the Japanese - he felt it would waste their strength which they needed to conserve to fight the Nationalists after the war. If the CCP becomes serious about fighting the war, then it is good for China but probably bad for the CCP overall compared to our timeline.
Lin Biao is unlikely to become a leader. He was not in China at the time. He was in the Soviet Union recovering from wounds from late 1937 until early 1942. Many of Mao's allies were not in senior leadership positions, and some that were seem to have been his allies more out of convenience or political calculation than out of conviction. I'm not sure who or what group would take the lead, but they will probably make very different decisions throughout the next four years than Mao did.
Mao was not only shrewd, but got lucky. As late as 1946, I would not say the CCP's ability to take China was very likely. The key was the strangeness that happened in Manchura in 1947-1948 which saw the CCP defeat the Nationalists militarily because of repeated and continuing missteps by senior KMT military leaders in Manchuria. Without Mao, I am very doubtful that can be repeated. My guess is that the necessary conditions for the CCP's victory simply don't happen without him.