I agree with OgNasty in that I think bitcoin would probably survive a short and specific 51% attack. By that I mean a 51% attack which double spends a handful of specific transactions, as opposed to a prolonged and sustained attack just mining empty blocks to censor the entire network, or something similar.

There are too many people involved in bitcoin who either don't care or don't understand the importance of a 51% attack, blocks being orphaned, or transactions being reversed or censored. Look at some of the "top" altcoins. Ethereum - not a classic 51% attack but effectively the same result (majority of hash rate reversed some transactions), creating Ethereum Classic in the process, which itself has been 51% attacked several times. XRP, USDT, BNB - completely centralized, can have transactions reversed or censored at any time by their owners. BCash - successfully 51% attacked. And yet all these coins continue to have volumes of billions of dollars and attract new users.

Provided that the 51% attack was short lived, and bitcoin continued to function normally afterwards, then there might be a hit to the price, but I don't think it would be the end of bitcoin.