Hi Sue
I'm so sorry to read about your sad loss this morning, it sounds like you were on your own there, but tried to do all you can for your chipmunk.
Reading your earlier posts, you still have one chipmunk at the moment, which I find a great help when I lose one.
I'm would guess your chipmunk had become infected by bacteria which reached the kidneys. Although I don't think there was enough time in your case, your vet could have taken a urine sample to see if this was the problem. A kidney infection can be treated by diuretic drugs or even a herbal alternative to flush out the kidneys.
For anyone else coming across this sad post these are some plants which can help:
Dandelion
Couch grass
Uva Ursi, also known as Bearberry
But, I am no vet, and no one can pin point the exact problem by email, so if you can ring around the vets in your area to see if there are any with experience of chipmunks.
Mybest wishes Sue.