Either he a big idiot or he just clueless about bancor protocol like you.
He would lost alot if he do that. The price will adjust with every token you sell(destroy by contract)
So the price he get will extremely low toward the end of the reserve remain. He would better off selling in exchange.
And for any smart token, to empty the reserve, you need to sell (destroy) every smart token that exist. It will eventually bring the price to zero.
For bnt that would be impossible as the bancor team hold alot and the token relay in the app also hold bnt, eventually it doesnt matter if every weak hand sell bnt. Relay and bancor team will hold it more