I dont think it will happen because ethereum and any other alt has a strong potential in the market and Libra coin is new in the market and it is difficult for libra to turn over the place of other coin even bitcoin,bitcoin is decentralized in the first place.
It is not about the potential that Etereum has, it is about the hard facts and these facts say that Ethereum is stronger than any other decentralized smart contract platform out there.
I agree, ethereum is basically good for business platforms and not as a currency like bitcoin. Likewise Libra Coin, will be used only on Facebook platforms such as WhatsApp or Messenger. Certainly Libra Coin will have many investors because Facebook members are in almost all countries in the world