The North Vietnamese are going to be in deep trouble; half of their war materiel came from the Soviets and the Warsaw Pact, while the other half came from the PRC. Any kind of U.S. and ARVN offensive to wipe out the NVA and VC base areas in SVN is going to be a lot easier (no cakewalk, given the tenacity of the NVA), but without resupply of ammo, spare parts, SAM missiles, etc., the NVN's war effort is going to sputter to a halt. And then it's Nixon's turn to tell Hanoi "Okay, ready to settle, on the condition that you give up conquering the South anytime soon?"
I read some stuff on the near-war in Grad School; supposedly Gromyko called Kissinger (he was National Security Adviser in 1969) and asked for America's position should the two Communist giants go to war. Kissinger said "give me a few days", and he went and talked to Nixon. Kissinger called Gromyko back a week later and said that while officially, America would declare its neutrality. But privately, we would sit back and applaud while the two Communist juggernauts engage in the greatest slaughter since Ghengis Khan (and slaughter there would have been).