What happened to cast of Hazel?
Herein, why was Hazel Cancelled?
Apparently NBC cancelled it when they left and it seems strange that CBS would pick it up with Hazel and Harold now living with Mr. B's never before mentioned brother and his family. Don DeFore and Whitney Blake didn't quit -- they were dropped from the show to save money (as you guessed).
Also to know, why did they change the cast of Hazel?
By the time NBC canceled the series in the spring of 1965, Hazel had fallen out of the top 30 programs. CBS picked it up for the 1965-1966 season, and made a number of cast changes. Buntrock remained in the cast as Harold Baxter; DeFore and Blake were dropped and replaced with Fulmer and Borden, respectively.
Hazel doesn't die (as in the book/movie ends before she dies she must die at some point because she is only mortal), Augustus does. John Green released on Twitter that Hazel died the year after Augustus.