If bitcoin will hit $6000 then it will probably end up with $5800 or $5900 ethereum can hit $400 but that does not matter there will be bounce for me.
Normally cryptocurrencies price should not be correlated to each other but most of the time, it just follows the bitcoin price, and I agree with you if BTC will drop under $6000, ethereum price will drop under $400 unfortunately.
With the market of bitcoin ethereum will be connected and when the market of bitcoin will drop then ethereum will also drop and $400 is not away from the current price of ethereum. The price will drop but it will recover back with the rising market of bitcoin. But it is also possible that from now the price of bitcoin and altcoins start to rise and the price of ethereum do not drop any more and will again reach to $1000