We never know what will happen in the future. Maybe if I say there is no altcoin that can replace bitcoin, it's really premature analysis. Who knows if one day there will be one or more altcoins that can beat the value of bitcoin, even if that's when. But for now, bitcoin is still the spearhead of other altcoins.
If you remember, in mid-2017 Ethereum came really close to toppling Bitcoin from the no.1 position. At one point, less than 2% in market dominance separated both the coins. But that was the closest any altcoin ever came in challenging the Bitcoin dominance. After that, at no point any of the altcoins could even manage 50% of the market cap of Bitcoin. Thousands of new coins and tokens got listed since 2017, and the situation hasn't changed. And I don't think that it will happen in the near future. Because there is limited room for the new projects, since the cryptocurrency sector is already saturated.