IMHO there are two possibilities. Either SE replaces all the explicit user names in comments by a generic name like
user... or they don't. In the first case, they will find it easy to also replace the explicit names in answers and so on. In the second case, our attempts to go through our own questions and answers to change the user names will be futile because we won't be able to edit the comments. Just deleting all the comments in which this user gets addressed is IMHO a bit too drastic a measure that could be taken.
I do see the point that a user can ask for all references to their (real or whatever) names being erased. Of course, it would be great if SE would offer such a functionality, not only when one quits but also when one just updates the user name. But this is not in the hands of individual users. Therefore, I would answer the question
Should we reformat references to deleted accounts?
addressed at single ordinary users with
At the same time, I would like to argue that SE should provide us with a function that allows us to replace all explicit occasions of our user name with some updated name. (Of course, I understand that this is nontrivial because user names are not necessarily unique.)