Yes, for most practical intents and purposes, the content becomes inaccessible to 99.999% of the humanity, and also to bots.
the data dump is in an arcane XML format, and it's not easy at all to connect a question with its answers
let alone that the vast majority of readers won't even attempt to download the data dump
nobody can resurrect the sites from ...
This would only be a problem if the comment now existed somehow at Ask Ubuntu. The behaviour here is the same as if you'd waited another five minutes before trying to submit your comment.
While technically there is a race here, it's only a "race condition bug" if it results in some otherwise illegal state.