Don't they have enough circumstantial evidence to convict Dale Smith already?
I know it's better to have a body, but even if they found her after all this time, there may not be any way to prove how she died, unless there were broken bones or something. I think he probably strangled or choked her, and I don't know how that would show on an autopsy.
So even if they found her body in some remote area, what difference would it make unless it pointed directly at DS. It's highly unlikely that she ran off to parts unknown, leaving all that was dear to her behind, so the assumption is that she is no longer alive and that she met her demise at the hands of Dale Smith. Unless LE is still actively following up leads and studying video's etc, I would like to see them arrest him anyway, and leave his fate up to a jury.