China will not help.
If you help your neighbor A, it is not because you have something against B and you want A's help. If your neighbor A's house is damaged by a fire, you help out of compassion and with no desire for anything in return.
For so often in international politics, that is not how countries interact with each other. We want an alliance with the Philippines. We give all sorts of aid. But precisely because we seek to contain the Soviet Union and/or China, we want an alliance with the Philippines. An alliance carries duties, responsibilities, and privileges.
If my neighbor's house got damaged in a fire and I helped his family, that does not mean I have incurred any kind of responsibilities for him and his family.
China is already busy and financially burdened in Africa to the point that some have called Africa China's colonial outpost. Does anyone here, particularly the forum's Filipino members, really believe that a US withdrawal will automatically bring in China as replacement ? Why should China incur for herself political and potentially even military duties for the Philippines ?
There will be no China-Philippines political alliance. China will do nothing other than sell the Philippines whatever Duterte want. Note I said Duterte, not the Philippines. As the Philippines weakens, she will decrease her influence in the SCS issue, leaving China stronger in the sea immediately off the Philippines' coast.
Duterte is being shortsighted and behind closed Politburo doors, China is laughing at the Philippines.