Ask yourself why did the North sign off on the Paris Peace Accords? Simple fact is that their supply network had been crushed and they had no way to continue waging the war.
No, how are you going to stop tens of thousands of guys with backpacks and bicycles ?
You can't.
They came back to the peace talks because Hanoi was getting pounded by the B-52's and they couldn't do much about it.
Their strategy became, "Let's sign off on the peace accords, get this bombing turned off and when the Americans leave, we'll defeat the ARVN"
