I understand that most people probably would switch. I’m actually looking it this from a different perspective: would Bitcoin be able to regain trust? A large hack might kill Bitcoin if everyone decides that they don’t trust Bitcoin’s security.
In theory though this would definitely cause some chaos if something like this happened today, I don't know if it's enough to kill bitcoin but it would certainly drop the price. Most people only interact with bitcoin in a very abstract way through exchanges and don't understand enough of the details to care. If the exchange switched to the proper chain and everything appeared to be fine to the end user I don't think you'd see too many long term problems.
These systems are nothing like PayPal and Venmo and investing in ignorance is just asking for losses.