Mao once said (probably in line with his penchant for saying ridiculous stuff to troll people with) that China was prepared for nuclear war simply based on its huge population. However in the 60s NATO had 30,000 nuclear warheads while the Russians had about a tenth that and even less that could actually hit America. In such a war Russia would have been literally wiped out and had the US attacked China too they might not have been totally destroyed as a people (China was not as urbanized back then as it is now) but the state would certainly cease to exist, unless you count Mao's bunker complex as a state.
Conventionally...it depends on how the Russians do in Europe. They had force of numbers as well as a really good blitzkrieg doctrine down. Given a solid Sino-Soviet alliance and reasonable war aims (continental Europe, East Asia, Finlandized UK, India, and Japan, more or less), I think they could've pulled it off.
China had some fortified industry by this point and the whole Communist bloc would've been self-sufficient materially. Vietnam and the DPRK would be on the Pact side, pretty much securing the Asian theater goals.