What's the current price of the altcoins compare to the ICO price you brought them because that will determine if you should hold or sell. As a rule of thumb for me, I never sell at loss. It is only weak hands that sell when price is below the price they brought. Definitely as you have rightly say when the price of bitcoin goes down that of altcoins also follow suit. I strongly believe bitcoin will still make that bullish run again it is just a matter of time... So the price of your altcoins will also rise to the target you have set if you can just be patient.