I was a fan of the show in the very early 80's.... I was watching it with a year old girl my Mom day-cared and asked her where Casey and Finnagen went. Her answer was simple "They died." I hardly doubt they were killed off, I guess it's like polar 20 said, the puppeteer wanted to retire.
Still, I wish they found someone else. To me it would be like replacing Ernie after Jim Henson died. You
I know this is 4 years old but I believe my father told me the way they officially did it on the show was that eventually Casey went to school. But the puppeteer wanted to retire, but that is how the characters were written out.
Casey and Finnagen's puppeteer moved to Hornby Island in the Gulf Islands in BC.