It probably stretches a bit but mine is 160k miles old and still fine. Or so it seems.
I think if I was bothered I'd swap it for a new once and change both cogs and the tensioner at the same time. But there are far more other things to worry about on a TD5.
Others may come on and comment, who have had more experience than me.
Or there is plenty of discussion here: https://www.google.com/search?q=td5...j0i22i30l4.4595j0j15&sourceid=chrome&ie=UTF-8