If you can break bitcoin, you can also break all the encryption we use for banking and other transactions, so might as well stock up on SPAM and ammo.
Centralized businesses will not suffer much and will switch. Blockchains will get destroyed due to their immutable nature.
For example BofA has ~70 million customers, 3,700 retail branches, if each has three tellers at any given time of operation (generous at BofA these days, where you'll usually find one) and is open 8 hours a day, and average time to serve a customer is 20 minutes:
3,700 * 3 tellers * 8 hours * 3 customers / hr = 266,400 customers / business day
70 million / 266,400 customers = 263 business days