Among 30 goal scorers in the NHL, I found only two others who fell to even 10 goals the following year without missing major time to injury, Morris Lukowich and Rosaire Paiement. In 1983/84 Morris Lukowich scored 30 goals while playing all 80 games for the Winnipeg Jets. The next season, while being traded to Boston in February, he scored 10 goals in 69 games. He was 28 in that 1984/85 season and would score 12 then 14 goals before retiring with Los Angeles at 30.
In the Vancouver Canucks' inaugural season on 1970/71, Rosaire Paiement led the team with 34 goals. The following year in 69 games he scored 10 goals at age 26. He would then jump to the WHA's Chicago Cougars and never played in the NHL again.
The two players that fell from 30 goal years to below 10 goals were Andrew McBain and Sid Smith.
After scoring 32 for Winnipeg in 1987/88 McBain fired 37 goals in 88/89. The next season, playing 67 games with Pittsburgh and Vancouver, McBain dropped to 9 goals. He played most of the next two seasons in the AHL then signed with the expansion Senators in 1992 where he scored 7 and 12 goals.
Perhaps the most drastic collapse for a 30 goal scorer was by Maple Leaf Sid Smith. He was named 1st Team All-Star in 1954/55 with 33 goals Smith and then was named captain of the Leafs in the off-season after Ted Kennedy retired. The pressure of captaincy was apparently too much for Smith. Although he missed 15 games due to injury he plummeted to 4 goals in 55 games. By mid-November of 1955/56 newpapers were picking up on Smith's lack of production. The Canadian Press had a headline saying,"Leafs are Minus 'Crucial' Scorer" and noted that "after 17 games this season, he's still looking for his first goal." The pressure was so much for Smith that prior to the next season a CP headline declared, "Smith Gives Up Toronto Captaincy". The article stated, "General manager Hap Day said Smitty 'obviously found the double burden of playing and carrying out the responsibilities of captain too much of a mental strain.'" In 1956/57 Smith once again played a full 70 games and climbed back to a respectable 17 goals. After 12 games the following year, he retired to play Senior hockey with the Whitby Dunlops.
One other amazing drop in goal scoring happened to one of the greatest goal scorers of all-time.
Joe Malone scored 24 goals in 24 games for the Hamilton Tigers in 1921/22. At age 32 he was traded to Montreal Canadiens in December 1922. Malone played 20 games predominantly as a sub and tallied only one goal all season. He'd play only 10 games the following season before retiring.