Until 1968, Vietnamese policy was to fight a 'protracted war', fighting the Americans and the southern forces wherever they could and with whatever they could, inflicting as many casualties as possible in an attempt to force the Americans out. This worked for a while but by 1967, casualties were mounting and the protracted war found its opponents.
Chief amongst them was Le Duan, chief of the Vietnamese Worker's Party (which would later become the Communist Party of Vietnam) who wielded as much political power as Ho Chi Minh. Le Duan wanted a huge military confrontation with the US, a decisive battle, that would force them out of Vietnam for good. They were not alone - other members of the Vietnamese political leadership and military felt that the US had not won yet and that the 'balance of forces' was sufficient that further offensives could win the war.
Aligned against them was Vo Ngyugen Giap, the Minister of Defence, who thought it was too early: Giap's overall strategic plan comprised three parts, resistance, general offensive, and general uprising, and he clearly thought they were still in the resistance phase of the war. Nonetheless, after he was overruled, Giap set to work planning the offensive, despite not believing it would be successful.
To answer your question directly, some parts of the Vietnamese leadership believed it would be a complete victory, that having inspired a general uprising in the south, would eject the US from Vietnam. Others felt it was not yet time for a major attack and the 'protracted war' should continue. Nonetheless, I should point out that 'success' and 'dissuade the Americans from further fighting' are one and the same thing.
In future interviews, Giap did say that the political and military aspects of the war were not separate, but were intrinsic parts to one another. The offensive's aim was not to actually push the Americans out but to persuade them that no matter how long the war, they would eventually lose. That being said, the historiography of the topic is a little difficult, as the offensive was a success, Vietnam did win the war, and the Vietnamese historical records reflect this. One province committee did say to its cadres that the offensive 'will win the war', but this is clearly propaganda. Even senior persons involved in the Vietnamese war struggle could express pessimism about the coming offensive. So when we look back, we have to work hard to separate what is propaganda from what was really expected.
In an interview in 1969, Giap said 'to prove their military defeat, I'll go back to their political defeat.' Whether or not he actually intended a military defeat is unknown, but he probably viewed it as unlikely, even if he thought the outcome would be primarily a political victory. The rest of the Vietnamese commanders - and we focus on Giap because he planned the thing - had a range of opinions, from 'the Americans will retreat from Vietnam' to 'it will be a disaster.'
I have to go unfortunately, but this quote perhaps summarises the issue:
"According to General Tran Van Tra, commander of Communist forces in the south from 1963 to 1975, the objectives were “to break down and destroy the bulk of the puppet [South Vietnamese] troops, topple the puppet administration at all levels, and take power into the hands of the people; to destroy the major part of the U.S. forces and their war materiel, and render them unable to fulfill their political and military duties in Vietnam; and to break the U.S. will of aggression, force it to accept defeat in the South and put an end to all acts of war against the North."
The Military Art of People's War: Selected Writings of General Vo Nguyen Giap (Russell Stetler)
The Tet Offensive - A Concise History (James Willbanks)
Tet Offensive 1968 (Stephen Badsey)
May I ask if any historians in this thread can recommend me to books about the Vietnamese revolution, particularly its political history, that are primarily from the Vietnamese perspective? Most books I find are extremely American-centric and are all military history.