a. As per coinmarketcap, currently the largest BTC market is the BTC/USDT on OkEx. On looking closer, 3 out top 10 markets are USDT (excluding Bitfinex). So that is nearly 10% of only BTC liquidity gone.
b. As Tether and Bitfinex are connected so the exchange shuts down. It is the 2nd largest bitcoin exchange. So all that liquidity vanishes too. That brings our above total to 15%.
c. There will be many cross connected trades relying on USDT so my guess is the liquidity number will be higher, maybe even in 25-35% range.
d. This will cause panic and people selling BTC left and right. So BTC prices taking a huge hit. It might go down as low as 1-2k.
e. Most other cryptos are pegged to BTC. So with BTC liquidity gone they will take another huge hit too.