First, Bitcoin can't scale if the rules aren't changed, the longer the rules don't change, the more Bitcoin Cash or another cryptocurrency will compete to steal BTC market share.

It is possible if Bitcoin Cash can be increased much higher than Bitcoin, but Bitcoin Cash has its drawbacks too. I think it's really hard to say whether Bitcoin Cash will take place from Bitcoin at this stage.

Bitcoin won't die anytime soon, Until the need for BTC is removed, Bitcoin will maintain a large percentage of market capitalization.