I personally can see a world where bitcoin's marketcap and activity is eclipsed by a future altcoin. Ethereum is getting very close. But in regards to "replacing" bitcoin, nothing will replace bitcoin. Bitcoin will always be the first cryptocurrency, it is the most decentralized coin and it is literally the underpinning of the entire crypto economy. Nearly all coins are quoted against BTC. This won't change in the same way the USD isn't going to be usurped by the yuan for an example.
Bitcoin used to have a huge 67% dominance but it's down to BTC 43.4% and Ethereum used to have 6% dominance but now it's ETH 17.9%, Ethereum is moving closer and so are the other coins like Binance coin, but it will take time before they equal or surpass Bitcoin's dominance, and I don't think any exchange will delist Bitcoin or make other coins their primary, Bitcoin will still remain the first and will not be out in the top 5, even if other coins are aggressive in their development.