Limited supply: Bitcoin has a fixed supply of coins of over 21 million that makes it not inflated and scarce like fiat currencies.
Potential adoption: Generally a massive number of business owners and individuals are accepting Bitcoin as a mode of payments thereby reducing it's demise.
I agree with you that bitcoin will always survive. The limited supply of Bitcoin creates a deflationary characteristic, where the value of Bitcoin tends to increase over time because demand continues to grow while supply remains constant. This can result in long-term value stability and maintain user confidence in bitcoin. Because limited supply can encourage further adoption and use. Scarcity and potential for long-term value growth is what attracts the interest of many investors. It is possible that bitcoin could disappear or no longer have value but the possibility is small. And I can't imagine that if bitcoin disappeared or no longer had any value, that would definitely have an impact on most altcoins.