The Korean War was the first proxy conflict of the Cold War, so if the Korean War never happened, then the idea of a proxy conflict goes untested, at least for a certain period of time. Also, the United States may send troops to support the French in Indochina, without having to worry about the stalemate in Korea, so American airpower could be used against the Viet Minh, though American airpower proved to be useless against the North Vietnamese in OTL's Vietnam War, so whether or not it would be useful in this timeline is up for debate. Even if airpower was useful against the Viet Minh, there was nothing stopping China from sending the PLA into North Vietnam to support Ho Chi Minh.
The PRC lacked the naval capability to invade Taiwan. Even today, they still do. I doubt the absence of the Korean War would change that. Also, fun fact, the Taiwanese Strait is extremely treacherous for most of the year, because of high torrential winds, except for two windows in April and October, respectively. These windows last about four weeks. According to PLA studies in OTL, April is extremely foggy and October has late season typhoons which hit Taiwan about six to seven times per year. If the PLA invaded Taiwan, then their supply lines are tenuous, again, because of the weather. There are also very few beaches on which the PLA could actually land on.