Well, he decided to leave us.
We found him yesterday in the same spot where he fell asleep - but this time he had crossed over. On a good note, we had fed him again the night before, so he went with a full tummy and lots of love. I think it was that comfort that made him decide to let go.
On the other bright side, we do have a full and proper set-up for a gecko now, so we plan on looking for another rescue/unwanted pet. Hopefully, the next one won't be as bad.
And yes, I want to smack the previous owner and starve her for awhile. She needs to know hunger and neglect.
