While I mostly agree with what he said, I think there are some things they could do to give users more control without "gutting" threads.
1. Allow accounts to be deleted, with all of all their comments and submissions reverting to a [deleted] author.
2. If conversations require author continuity, anonymize the author per-thread to something like the Google docs anonymous usernames
3. Include a deletion request with clear guidelines for reasons why something can be deleted.
Of course they won't do these things because 1) it's only two people and these features will require development and maintenance 2) an opaque and uncertain process ensures that they'll only receive requests in the most necessary cases 3) people might think more about what they write if they can't easily take it back
What they could really do is add a warning to the account creation, submission and comment forms telling users that their submissions are not retractable past the grace period.