There's nothing specific about Bitcoin in what happens if Tether is shown to be a sham. Anyone who was using Tether to trade in and out of another crypto will get screwed of they are out at the time the music stops playing. That will reduce demand for crypto and reduce sell action - unless people pick another crypto as a safe haven. I reckon that mostly speculators have been using USDT etc so perhaps that will be good for crypto long run. Of course any exchange left holding a bunch of Tether may go bust too... I wonder what their out is?