Hope BTC-->LTC replacing will not happen but history teaches us that the most markable events occurs when nobody expects it - https://en.wikipedia.org/wiki/Black_swan_theory

Crypto is at its infancy, nobody knows which one is going to be the one that emerges like the heir of fiat. There might be a third one that has not yet been released yet that could overthrow bitcoin, litecoin and the other alts alltogether.