I have seen a few Allied players skip the Flying Tiger attack. It is not a move I agree with. I will sacrifice Japanese planes I CAN REPLACE to take out that plane that can not be. It gives China a chance at offensive attacks and some defense.
I see no reason for Japan not to attack China. While killing all the Chinese troops in round 1 of a '41 game can be a bit of a stretch, the flying Tigers and some other territories should be attacked. While Japan may not want to spend the effort to totally eliminate China it is worthwhile to reduce them to just Chinghai. This way they can not produce any troops and are no longer relevant.
From the Allied side it is worth Russia’s troubles to send some forces to China to delay the Japanese. If China can be held to 2 or 3 territories they will produce free infantry and increase the amount of forces Japan has to commit for an advance through the central Asian front. In most games Russia will eventually have to retreat it’s forces as the Japanese become too numerous to hold out over China and its infantry, but again the whole idea was to delay Japan anyway. As far as other Allied liberations occurring these are very rare. Normally this will be done by the US and it will also normally be after all the high value UK territories and the Philippines have been liberated.
I would say just come to grips with the reality that China is a good idea badly implemented in AA50.