Ah, why not laser guide as back up?
Because the TOW is a wire guided system, optically tracked. It derives its control signals from the wire. But still, its rated range and flight time at range is 6 seconds short of what the story mentions.
The next question would be just how long the fuel lasts. If it runs out of fuel at that same point, what would the velocity loss be and what would that effect have on any penetration performance?