oh yeah, that's scary stuff. heard about a guy who ran over a puppy in the middle of nowhere one time, and decided to shoot it in the head since he couldn't get it to a vet in time. he took the body to the vet so they could dispose of it, but it woke up in the freezer hours later. this story i think i remember hearing on local news. crizzazzy. poor things.
anywho, water is def more important than food in case of starvation, but yes, try weekend blocks. i doubt that 3 days of no food killed your elderly rat cj, but i'm sure that it didn't make him feel any better, and probably compounded some age problems he already had.