Depends on the way it unwinds. If it's through selling BTC to cover Tether redemptions, sure, that'd be bad for cryptocurrency prices. I have a feeling that it'll unwind like Mt. Gox, though - people who accepted Tethers or put deposits into Bitfinex wind up holding the bag when the fake money goes "poof".
You’re talking about two different markets. A Tether-USD is not the same as a USD. If anything, the fact that the irredeemable USDT even has value is a sign of the insanity playing out in the cryptocurrency market. A token worth 1 dollar but not really worth 1 dollar makes no sense at all.
"market cap" is a very bad representation of the overall value which is impossible to actually estimate. try selling 600 million worth of btc and see how that cap changes.
You can't compare money and market cap directly. Millions of dollars can move the market cap by billions. It's because the books on exchanges are relatively thin.
