Everything is possible. Nothing is indispensable in this world. Even the strongest and wisest king can be dethroned. But the task of overthrowing bitcoin would not be easy for any alt which wishes to snatch its throne. Bitcoin has already established itself and a solid community which backs it up. Yeah, there are actually a lot of coins created that are better than bitcoin in terms of features, like ETH which transaction confirmation is more speedy than BTC and XRP which is a lot cheaper, but bitcoin stood invincible ever since. Currently, I've no idea what could possibly lead bitcoin to step down from the limelight, but it doesn't necessarily follow it won't happen so we shouldn't discount that possibility. Better hodl both bitcoin and good alts to be safe.