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.
The case you say is possible when libra has too many connections with the crypto world, and we are also clear that bitcoin is the one that gets the most attention, with the success of libra coin, which will be free advertising and help bitcoin get more investors. However, if libra does have too much success, I feel this will be a threat in the future of bitcoin because governments of countries do not like underground activities in bitcoin, they need publicity, and libra coin probably allows them to do that, the government will actively support libra coin to compete with bitcoin