Clayton Woodworth died in 1951 and he had been sick for some time before that. I would guess that the Watchtower campaign against aluminum declined significantly when he ceased his work as the editor of the second magazine, probably when the magazine changed its name to Awake! in 1946. Also, Charles Truax Betts died on December 19, 1959, and much of ideas on aluminum published in the magazines were his own.
I just searched through the 1949 Awake! and found 41 mentions of aluminum. There was an article in the August 8, 1949 issue on Dr. Betts and aluminum poisoning ("Inside Story About Aluminum"). There were at least 15 mentions in the 1950 Awake! (with only one allusion to misuse of aluminum). I could find only 3 mentions in the 1957 Awake! (none of which concerned health). There were 6 mentions in the 1958 Awake!, one of which states that aluminum-ware is "taboo" in one claimed cure for cancer (April 8, 1958, p. 19), and another which gives a positive reference to "cakes of silver aluminum silicate" used in water desalination (September 8, 1958, p. 12). There were only 2 mentions of aluminum in 1959, and both were neutral. In 1960, there were 3 mentions, all neutral as well. It seems that the campaign against the health hazards of aluminum was pretty much stopped between 1950 and 1957.