there are two possibilities that will happen later.
first altcoin go up. This only applies to good altcoins. like ethereum, BNB, and other altcoins that have a large marketcap.

secondly, altcoin can die. This applies to all altcoins. if bitcoin goes up even more than 100% when halving later. then the dominance of bitcoin will rise. in the end those who hold altcoin will definitely exchange it for bitcoin. and the impact nobody else wants to buy and hold later.