I do not think bitcoin will be destroyed if the Libra coin is successful, on the contrary the success of Libra will most likely jack up the bitcoin to become bigger and higher in price. bitcoin is limited in number if the more requests to buy of course the higher the price and if libra is successful the crypto users will be more and it will affect the price of bitcoin to be higher.
bitcoin is currently the king of crypto and will not be easily replaced. maybe until the next few decades bitcoin will remain the king of crypto.