From my understanding of the military consequences, the Tet offensive was as a failure. The North Vietnamese lost tremendous materiel and manpower for little lasting gain....
The only way the Tet succeeded was politically, because it had definite shock value and was heavily televised. The US population and political leadership was so discouraged by the event that it became a watershed event for a country tired of inconclusive warfare.
In essence, from a purely military standpoint the Tet offensive worked a lot like the Ardennes Offensive of 1944 -- it got fixed assets out into the open so that superior firepower could be brought to bear. There will almost always be a delay in amassing those superior defending forces, which gives an initial impression of offensive success even when their eventual defeat is certain. In reality, those German assets would have cost far more time and casualties to defeat had they remained on the defensive.
In that light, a Taliban Tet would only be dangerous to the degree that the Pakistani forces are truly outmatched (in materiel or espirit).