That’s not how international obligations work. Most borders were defined at gunpoint but we generally don’t allow for arbitrary redefinition when the loser gets uppity, Crimea aside.
Infact all other concessions except HK and Macau were returned to Chinese about the end of the war.
It’s also unclear why Taiwan should be “recovered” at all, they were two factions of the cultural revolution sure, but that doesn’t mean they should be unified now any more than the UK should “recover” America.
we can of course disagree with china. but ignoring what they want is...i don't know...naive?
If one day situation permits it, Canada will become 5X US state.
The laws of man, including international law, treaties and borders, are made up and can be change with enough will or force.