It's an inhabited island with a military base and an airstrip; I don't see the Philippines just walking away. Moreover, both Taiwan and Vietnam also have claims on the island, not to mention that the US has no desire to see any part of the Spratlys leave its sphere of influence. China might like to confine the repercussions of a military capture of the island, but that relies on intimidating all the countries I just mentioned, which I do not believe it can do.