We had a wallaby a few years ago. One day it was really hot, we were out to brekfast. She obvisouly didn't drink once we got home and we pulled her out of the pouch in the aftrenoon to check if she was okay.
She just flopped. We freaked. rang the vet, they said don't bring her in, all they'll be able to do is charge us to tell us she'll die.
My mums partner at the time used to be a cattle driver and used gatorade to rehydrate animals if they needed it.
We gave some to Sheila, put her in a cool room and she did get better. I thought she was too far gone but she did recover, we mxed it into her water for a few days after.
Maybe not the best thing but we didn't know how much time we had left and we were driving past a shop at the time.