I don't think that if a 51% attack happens, then the coins in addition to Bitcoin will live, immediately a panic will start in the market and everyone will sell Bitcoin, because no mistakes should occur, and canceling transactions is quite the opposite of what Bitcoin was created for.
Of course, maybe in the future there will be a new coin that will be protected from such manipulations, but it will take at least 5 years to restore trust for people, I think so
The Hash Power Migration since China crackdown causes a drop of more than 51% of total hash power from the peak. If any corporations, person can collect all those hash power, it would give that entity enough hash power for 51% attack.
It is impossible to collect all those ASICs into one entity. In the past, there are pools from same owners that had more than 51% hash power but they did not do any attack on the network. Because it will cause harm for Bitcoin and for everyone. It is stupid to run 51% attack.