Correlation is not causation. And your mental model of how the cryptocurrency markets work is likely way too simplistic--did you know that cryptocurrency perpetual swap derivatives clear over $350B in daily volume?
Pretend for a moment that Tether pulls a Nixon, and closes the "dollar window" ending redeemability. Then what would be the difference between Tether and e.g. the BitMEX XBTUSD perpetual swap contract? Just think about it for a while.