Nah there is many way to unroot US-Japanese alliance, there is no permanent friend only permanent interest. China has nothing to lose on both scenario:
1-If Japan wants to remain US's lapdog and let let US dictate it term over Japanese future, it's nor really our problem, in fact we're glad that US will keep Japanese ambition in check by control them, a loose mad dog can be a threat to Asia as in WWII
or
2- If Japan choose to be independent from US and be neutral, China and Russia will likely have more security cooperation with Japan and restore Japan dignity as a free nation and be master of itself, as consequence US will have no place in Asia and less threat to China & Russia.
And you know why Japanese were so scare when High level military talk between US and China, they're afraid that
China and US is collude at Japan expanse, most likely US knew Japan is not so reliable alliance after got nuked by US and Japanese will seek revenge in event of their independent so by cooperating with China US will gain China's support to let US keep continuing control of Japan.
Diaoyu Island can be settle peacefully or by war all depend on Japanese attitude and relation China, we're not losing our sleep about it, and now China become stronger and stronger with bigger military defense budge, this island will likely settle in our favor, time is on our side.
Cought! Cought!
Red river ring a bell? tightening the water valve and Vietnamese will have hypertension and if we decide to reclaim more land in SCS , Vietnamese will double their blood pressure
...I know you guys have nightmare at night over China...and that's not the way to comfort yourself.