Unfortunately, two of the dog's voice-actors have passed away: Richard Mulligan
(Einstein) in 2000, and Roscoe Lee Browne
(Francis) in 2007.
Neither of them were ever well recognized in the movies, but Mulligan won an Emmy or two for his sitcom "Empty Nest", and Browne was well-known for guest spots on many programs, netting an Emmy for his appearances on "The Cosby Show".
A sad addition, veteran comic actor Dom Deluise(Fagin) passed away in the summer of 2009.