Counterinsurgency is a long and difficult method of defeating an armed opponent. Not only do you need to juggle effectively between military action, political action and civic action - you also need to aware that you're in for a long term commitment.

The United States strategy meant that the VC were never truly close to defeat. In counterinsurgency, you do not win by killing as many enemy combatants as you can. Unlike conventional warfare, in which victory is measured by how many battles you win, how many strategic objectives are taken and in overall, on more "clear" objectives. Unconventional warfare, as in this case, is far more difficult to define in simple terms whether you're winning or not. Many people are going to point to the aftermath of the Têt offensive and say, "The VC was broken, defeated and if only.."

No. Had this been a conventional conflict then certainly, it would have been a huge loss and the US would only have had to go on the offensive for the final victory. However, the truth is that the United States strategy in the Vietnam War was downright awful and not fit for the environment in which it was fighting. There was no priority in civic actions, for example, and no coordinated overall command. The US made too many mistakes in the war to allow the VC to be defeated. Some of those mistakes were committed choosing a strategy entering the war, some of those mistakes came from the very conservative culture of the US Army and its stubborn desire to keep their original doctrine.

A counterargument to the US use of conventional warfare in an unconventional environment would be to point to the conventional movements of the main force VC during 1965-66 which bled them badly. But even then, they did focus a lot on controlling individual hamlets, either through violence and terror or by their version of civic action. They had a constant presence there while the US did not. While the Vietnamese use of the Maoist guerrilla theory was very fluid, the main force VC would stick themselves to guerrilla warfare for most of the war ('65-66 and the Têt offensive in '68 proved to be the exception rather than the rule) while the PAVN would try to enter the conventional phase of the Maoist guerrilla theory with disastrous results in 1972 (the Easter offensive) and with far more success in 1974, by which time the US were gone.

Note: While we don't allow historical what-if questions, the core of what OP is asking can be addressed in terms of what the Viet Cong's situation was during the war, so this question isn't being removed on those grounds. So, you're good here /u/nicksam112.

For commenters: Keep in mind that if you're going to answer OP's question, it has to be based on the history, and not your guess as to what might have happened.