I don't think bitcoin will die. If you observe it everyday, it is gaining more investors and user base. More country is getting open in accepting bitcoin transactions, and more project and development is observed. Even if bitcoin power decrease due to a more popular altcoin in the future, it will stay alive because of the baser user it established.
Yeah it just keeps growing and getting bigger, maybe bitcoin will not be the main currency but I am pretty sure we will have some kind of digital cash perhaps an alt coin as main currency
Altcoin can never replace bitcoin for sure, bitcoin is mother and father of all cryptos and I don't think any other coin has potential to take place of bitcoin in future.