People, things are not complicated, this is not some kind of natural disaster, what is happening is that scammers at Scamfinex have to produce 1 US$ for every 1 USDT they produced out of the thin air, or they will go to jail. No matter how low the price is, they have no choice but to sell BTC, there's no other way they can produce US$. Point is they can not sell your coins, they can only sell theirs. It's that simple, why would anyone care if they loose the whole sum they've acquired through scam? They can either sell enough to cover the scam, or fail and go to jail. Sooner or later they will run out of BTC and the line will be drown under, their BTC will be in someone else hands, but your BTC will remain in yours. It's that simple, as someone said 1 BTC will always be 1 BTC, there's no reason to fear of their failure. Only way you can fail is to sell your coins, otherwise you can not lose because this is not your game that is happening right now.
If any of this conjecture were true, Bitfinex would be trailing in price not leading.
Why do you presume they are selling on their own exchange? They are in position to move fiat between the exchanges, which their customers can not do as easily as them. If you were in their place, wouldn't you do exactly what they are doing to cover the obvious?