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.
you are right. bitcoin is currently the highest existing coins and other coin I think was trying to imitate bitcoin. I think that the day would never arrive, because most of the major investors, investing in bitcoin, and it will make bitcoin prices continue to increase. if there altcoin emerging, and has a high price, then the price of bitcoin will also rise.