We just had a customer escalation caused by exactly this. One group relied too heavily on tribal knowledge for code reviews and didn’t want any other process. Once the tribal elders were gone, no one knew all the things to look for, and there was no other way to catch issues

As a Continuous Integration and Test guy, I was standing in the corner yelling “I thought you were DevOps. Where’s the automation?” Fine, Puppet/YAML doesn’t work with a traditional build and test, but you could have done syntax validation and schema validation that would have caught before the code review could have happened (and I showed them how a year ago, even offered to do it for them) and set up some monitoring to discover when you break stuff, before customers discover it.