Ok let me rephrase: It's not possible to lose the money. It's possible to cover-up what happened because the authorities aren't really investigating it. The money isn't lost however. The trail exists.

It would be possible to lose money if the money was in cash form. But given that US M0 (coins and paper money) are multiple times less than the trillions mentioned, this means that the money can only exist in bank accounts. And bank accounts are like the blockchain in a sense, but more centralized. There always is a trail. Source=>Destination. Money lost is not the same with "we aren't really looking or investigating it".