I do not think that this will happen, the bitcoin is way too big and I do not think it can be replaced anymore by another cryptocurrency.
anything could happen , so do about this bitcoin could be replaced as the most used cryptocurrency. so far i can see the most threatening altcoin that have a lot of potential like to make bitcoin not popular and people start move to this altcoin. they are ethereum they have one billion market cap while bitcoin have 10 billion market cap , this is possible but the chance itself just a little to happen.
usually when you see around here that people are talking about bitcoin and bitcoin dying, being replaced, ... they are in fact talking about an altcoin they want to advertise and this is the only reason why i always say a big fat no to these kinds of topic and say bitcoin is not going to be replaced by their shitcoin.