Cessna can't shoot it down if it's headed somewhere it doesn't need to be.
What's a missile going to target well enough to blow up on or near it? Bullet holes would take forever to deflate it effectively, and those bullets end up somewhere.
Seems to me a pyro disconnect device on the blimp end of the tether/umbilical with radio detonation and/or automatic separation on loss of signal through the cable would have at least left the cable in a relatively safe area instead of dragging more than a mile of it across the countryside.
So yes, the solution is detcord.