I'm not sure if BTC goes to 100k USD the price of ALTS will be 0, it's still very far to do that,
altcoin so far is also needed to be an alternative if someone does not use BTC to become a payment.
some people will also choose altcoin to be an investment if they don't want BTC, and as long as these two reasons are still present, ALTS will continue to exist and prices will rise over time.