It was predicted long ago that most of the altcoins in the crypto market will crash once BTC begins to gain dominance in the market. Its always good to hold only those coins that have real world applications and advanced and unique technologies. It was predicted in early 2018 that 75% of the altcoins will fail and cease to exist. Maybe the prediction is coming true. Just hold well established coins which have real world applications and you have nothing to worry even if BTC dominance reaches 80%.