The Allies certainly have the option for waiting until turn 2 before stacking Yunnan if Japan fails on J1. The Chinese will easily have enough units to retake the territory and likely will just use minimal forces if Japan did not issue a DOW on J2. at the end of their Chi2 turn, they easily could have 14 infantry + 6 art + 1 fighter stacked in Szechwan. That is an impressive army against the weak Axis forces in Asia.
If this is a no-bid / non-mod game, the Axis still can come back to win the game by capturing Moscow or heading down into the oilfields. I don’t think that I could come back for a win with BM rules.