Is it possible to define an activity status to be the equivalent of completed?
The status of an Activity is where it stands on its path from creation to completion (started, in process, awaiting xyz, etc, etc, completed).

In this flow, 'accepted' and 'denied' aren't statuses, because they don't tell us what the next action is (or if there will be another action). We should think of these as outcomes. Assuming the activity is a proposal or similar, what about creating a custom field called Result or Outcome, with 'accepted' or 'denied' as the available options?