I think you are referring to late deafened who had hearing speech skills prior to loosing their hearing, aren't you? They will, indeed, develop what is known as the "deaf accent" over time.
But someone like Shel, or my son, or AlleyCat that learned speech skills while they were deaf will often not deteriorate without "maintenance therapy." That is the SLP's hook to keep you coming back. My son hasn't has any speech therapy since the 6th grade and that was only one hour a week. His skills are the same, if not better, than they were then.
