Republic of China 1912 to 1973

  Ah he said theoretical territory.  If that's what its territory according to communist China then Taiwan is affected, along with quite possibly a lot else.  At the most extreme this includes claims on large parts of southern Siberia, which would definitely upset the Soviets.

  If its not then you immediately get something of an international crisis.  Expect Taiwan to invade to 'unify' China and start bring it up to date possibly supported by the US while the Soviets will probably make a bid for Manchuria at least.  Even if they don't N Korea would probably do it for them.  Also you might then have 1973 Hong Kong and Macao suddenly alongside 1913 China.  Not sure what would happen with Tibet?

  Well its already pretty much won the war and can still be supplied with weapons by the USSR.  As such it doesn't need China and such a weaker and older China isn't going to be a threat.  I don't think it would try and extract land from China, although if a major war developed over control of China between the Americans and Soviets they could end up acting as a Soviet ally or at least a resources base for Soviet operations.

  The interesting thing might be what does the west do.  OTL they for quite a while in the 1910s and early 20's possibly recognised the government in Beijing rather than Sun's KMT government.  One complication here is whatever the young Chiang Kai-shek is doing at the moment the old one is still alive and running a fairly unpleasant [by 1973 western standards] dictatorship.  Whichever government the various powers support, if any, will have an affect.

  That's the problem with mullauna using "theoretical territory of China" without defining it.  Just using China in itself would have been confusing as well so he probably tried to make it clearer but there is still uncertainty as to what he means.  You could have also the Shanghai International Concession included as well and more noticeably there is the question in 1912 of Tibet and of Manchuria with the significant Japanese influence there after the war with Russia.  I expect Manchuria is definitely included in the area affected but not sure about the others.