It would be fairly rudimentary (in context!) to fit such a device with sensors against certain intrusions (e.g. loss of balloon pressure) which would then trigger near-instant self destruction of electronics.

I would be quite surprised if such a high tech spy device did not have such contingencies as part of it's design.

And suspect it's probably one of the reasons why the risk of an overland shootdown wasn't taken - that is, there's no point risking collateral damage from falling debris, when you know the device will be programmed to wipe itself of most useful information upon being physically compromised.