and you think no other countries will get involve in someway? japan, SK, S.East asia, US.
if philipine ask for help. US very likely will send carrier to that region, just like taiwan 1996. its in US interest not allow china to control the entire south china sea. in that case US might use vietnam to counter china. just like when US use china in the 60's to counter USSR.
In my opinion, IF China gets into a conflict in the South China Sea, the US would/should be more then happy to stand by and watch, instead of getting involved. Washington knows fully well that China benefited mightily from all the conflicts the US is involved. Not directly, but indirectly by wasting so much time and resources in all those conflicts while allowing China to grow unchecked. The US would be more than happy to do the same and watch China wasting some of their money and resource on some insignificant conflicts.
The US might sell a few weapons to those nations fighting China and make a few bucks, but that's pretty much it.
In the Cold War, the US and the Soviets never faced each other directly even though the tension was huge and confrontation was very open. Avoiding direct confrontation was to prevent escalation of conflicts to WWIII. The same strategy would also apply between the US and China, with even bigger constraint because any confrontation between the US and China is not open. On the surface, the US and China are not enemies. So it has to take much much much much much more than a few islands in the South China Sea to get the US and China into a fight.
As to SK and Japan, they would not get involved if the US stays out of it. Historically, there has never been any meaningful relationship by SK/Japan and South China Sea nations. If any, there is tension. So why would SK/Japan get into a fight and risk their national interests for a few islands and those nations they hardly care about? Japan may want to have some of those islands for their own, but they are not worth getting into a war with China. They would be much happier standing by and watch the show.