I believe that no other altcoin has been able to replace Bitcoin, simply because they lack the mainstream adoption necessary to keep moving forward. After all, Bitcoin is the original cryptocurrency with first-mover advantage on the market. It's not simple to take down a cryptocurrency that has been used by many people for years. Despite many altcoins being superior than Bitcoin in terms of technology and features, they still lack the branding and trust Bitcoin has obtained since inception. For this very reason, I believe that Bitcoin will continue to reign supreme for many generations.
Unless another breakthrough technology comes into inception with the promise of overcoming crypto's existent limitations, Bitcoin won't be going anywhere. It shows us that altcoins are simply copies of the original Blockchain protocol (Bitcoin), unable to independently rise on their own. With Bitcoin's limited supply, and an ever-increasing demand, the possibilities of altcoins replacing it becomes one in a million. Just my thoughts