Aren't there three stages of a downded hanger? When it's first knocked out, it flames with smoke, then it flames without smoke, then no flame, then it pops.
You could code the barage balloons the same way. When they are first destroyed, they should disapear. Then they should reappear close to the ground, then they should spawn a little higher, then spawn again at full hieght. Of course they should be indestructable until they are completely respawned, or not, I haven't decided yet.
You could concider this a punt if you wanted, but I feel that barage balloon are a historic necessity for AH and I want to keep this topic current.