China in the Axis would mean big win for the Allies-it probably means Japan in the Allies camp or friendly neutral(but hard to see it).
In all the Chinese state at the time required enormous decade long efforts in order to rival Japan or Western powers. It has neither Navy nor ability to create one to challenge Japanese islands, and the Korean peninsula is in good defensive position. The colonial holdings in Indochina, Hong Kong could be threatened but further conquests are unlikely. Australia, and to lesser extent India are quite safe.
This means that Allies from the start of the war(if it happens in similiar way as in OTL) are in great position versus Germany-most of the Pacific fleet of the British Empire can be directed to defense of Atlantic and Britain. It would make the naval battles that were happening in OTL easier and shorter for the Allies. Air assets and pilots diverted from Pacific that were there in OTL would also lend a hand in Battle for Britain.So in all the Allies are in better position then in OTL. Also expect battles for Africa to be shorter with more troops from Pacific available.
SU is in slight disadvantage-as Germans might abandon plans to invaded or seriously fight England and focus resources spent there in OTL on attack against SU, and Chinese army might pose some disruption.
But in all it wouldn't face destruction, only some smaller gains postwar.
An interesting case would be Japan if in Allied camp and its postwar fate as fascist state with racial doctrine.
Starting point here is from story line
The Centre Cannot Hold: China during the Warlord Period 1919-1929
1919 - the Year of Revolution:"
. what about 2 Decades "time required enormous decade long effort"
A China does not need to build a Traditional Navy with Battle wagons and the like to threaten Japan,
Subs and shore Based Aircraft would can do that , now who needs a place to rebuild a Aicraft Design and Building infrastructure Oh the Germans, maybe they can help.
Who will need in the years to come a place to Build new Prototype Subs out of the eye of the Powers in Europe , Oh Germany again.
Germany will need Raw Materials who might have some they need (damn long way to get them, But if being handed out Cheap might be worth it) Allot of this China has, (I am talking Trade as both nations strapped for cash )
But China will need to build its Infrastructure up again were to get some of the best Engineers and Trade school experts.
This is a Period that the Soviet Union is rebuilding almost from scratch with an Infrastructure almost as in bad a condition as the Chinese and they built that up with very little outside help. If China Can rebuild 1/3 as well as the USSR did between 1919 and 1939 she will be a Industrial powerhouse to compare with Japan at least. Big ask but possible and I am thinking far from ASB
Germany is also a wreck but has a number of things Chinese Military might find useful like disused Ammunition Factories and little things like all the Tools for Making a 77mm field Gun, say they go as scrap to China yes get reused, This is a possible ally that might be more useful in the long run than the Secret Testing grounds the Germans built in Soviet union and the Tech Trade would be more useful.
Biggest obstacle Distance and Logistics, But this has a up side also in that China is unlikely to be seen as a threat. Japan after all did not really start drifting away from the allies till the Washington Treaty a couple of years away
Just having a Market that will buy German Machinery even on a small scale at first, would help Germany Economy after the war, Also the Italians admired and worked with Chaing OTL
All that and a Germany that is important to the rebuilding of a Proud China might be able to pulls strings and influence than Germany had with Japan.
And one big thing China can build without getting into problems with the US, that is isolationist without those big navies. Who said a US will even come into a war in this timeline in fact a better performing Less corrupt China is better Market that might be more important and still friction between US and Japan, China with no powerful Navy and Force projection.
China does not need powerful Navy to threaten the European Empires, And might seem little threat to the Philippians, Unlike French Indo Chino Malaya and Burma.
Start small even a Couple German Pilots and ground crew say Fokker ( Anthony Fokker will sell to anyone to restart his business and good German connections ) built aircraft, and 3-400 German advisors ( there a so many disillusioned German Troops with skills and no jobs, you get a good Cadre for a 10,000 strong force )