We are talking about a hypothetical case here. Since the liberation of Taiwan would be an continuation of Chinese civil war, I put less than 40% chance of UN involvement as UN force didn't intervene in mainland. If soviet provided air support over Taiwan strait like it did over north Korea to counter US airpower or managed to limit US full involvement by transport PLA soldiers with its ships, I think PRC could have a 50/50 chance. After all, PRC concentrated over 500,000 soldiers in provinces across from Taiwan.What is “might have” what are the odds. What is the extent of Soviet support and American intervention? Air, Naval, amphibious forces matchup and logistics? These require careful calculations not just bravado.