The study mentions that there is no degradation in "voluntary memory", only in "intrusions", which they define as "Persistent, distressing involuntary memories"

The study mentions that there is no degradation in "voluntary memory", only in "intrusions", which they define as "Persistent, distressing involuntary memories". This study specifically measured only the first week after watching a trauma film, so I'm sure you're right that the extension of this to actually treating PTSD will be a lot more complicated, but it doesn't sound like the treatment is expected to cause complete forgetting of the event.