Nobody knows if BTC will be the king forever. I think it has two big advantages that will never go away: the developer is anonymous and has never cashed in his shares, making it not about the profit at all. Two, it was the first cryptocurrency.
However being first doesn't make it the best. It has lots of shortcomings and in the end the argument is "everyone likes it so everyone should like it". There's new coins that have better performance, efficiency, security, etc.
It's entirely possible another coin establishes itself as the best and the market follows suit. For instance if ETH 2.0 comes out and sees big adoption, low gas fees, low power usage, faster blocks, etc? Or another coin? All it would take is some consensus and off it goes.