For the North Vietnamese, the Tet Offensive is both a military and political failure in Vietnam. The "general uprising" they had hoped to ignite among South Vietnamese peasants against the Saigon government never materialized. Viet Cong had also come out of hiding to do most of the actual fighting, suffered devastating losses, and never regained their former strength. As a result, most of the fighting will be taken over by North Vietnamese regulars fighting a conventional war. Tet's only success, and an unexpected one, was in eroding grassroots support among Americans and in Congress for continuing the war indefinitely. One other benefit for the North Vietnamese from Tet was that the Southern VC leadership was decimated. The Vietnamese Politburo put loyal North Vietnamese troops into surviving VC cadres to make sure they stayed in charge.
Actually winning would have been better for them but there was some 'heads I win, tails you lose' for the VC.