JW411 and spelkesoftly:
You are both correct. Since I typed my original contribution above I have discovered this website:
http://www.argosyair.com/index.html
The individual aircraft histories it contains show that most airframes were in MUs by the early 1970s although some were still on the go for a few more years. So Mr Healey's 1977 axe was NOT to blame for the en masse demise of the Argosy .
This website is comprehensive and well worth a visit.