Premise: Yogi the Easter Bear is a 1994 animated television special starring Yogi Bear and produced by Hanna-Barbera which was broadcast in syndication on April 3, 1994. This was the last time Don Messick voiced both Boo Boo and Ranger Smith (his last being "Arabian Nights" which was also first aired in September 3, 1994). Messick died in 1997.
Hypothesis: Messick died after voicing Ranger Smith on the final episode of the last season.