I agree with SWJED that the most costly result of renouncing Taiwan to garner support from China is the damage this would cause to the U.S. reputation with allies. Nations like South Korea, Japan, Australia, and India would wonder if the U.S. would "abandon" them given the need. Additionally his point regarding the difficulty of forming any sort of Sino-Korea-Japan is very true. The Japanese and Chinese are long term competitors in the region and the Koreans have long resented the Japanese for their past exploitation of Korea.

Secondly I disagree with Stu-6 as to the threat Taiwan faces from China. China truly believes Taiwan is a part of China. If China believed it possessed the capability (which it is rapidly building) and the opportunity to reintegrate Taiwan under mainland control they would seize it. This would not necessarily entail open warfare but could be accomplished through threats or even a blockade if the U.S. made its intent to remain uninvolved clear.