The war would have ended in 4 to 6 months by invading and taking the North and extending the front across Laos facing China against infiltration from surviving NV troops and the Chinese.
Lame brain and idiot LBJ was wrong. The Soviet Union would not have started a nuke war over Vietnam. They ain’t that stupid.
It would have stabilized the South and the North could have been pacified and the probable reunion of the country, but the US would have to commit troops for an undetermined period to keep the peace.
The war was never going to end without regime change in the North and Kennedy/Johnson/Nixon were utterly unwilling to face that.