BTC is the king of crypto, so yes, if btc crashes it does effect all the market, basically people start selling all there holdings in panic and cashout there investment in loss resulting in overall reduction in the market cap.
I was also thinking same up till last month but somehow I have changed my point of view. Because even when btc was falling, there were some altcoins going higher. That made me think that even if btc crashes, there is still chance that solid coins can survive.