There's a few reasons why he could have passed away. One is that the vet gave too high a dose of antibiotics to him, causing him to walk funny and bump into the cage. Another thing I noticed is that you seemed to have placed them in the same cage together, at least in the beginning, when he was trying to escape. That is going to cause stress on him - then it looks like you moved the female out of the cage (which is a good thing!), but placed her in the cage next to him. Could they still see each other? That could also cause stress. Finally, you stated that your female sleeps in the dim light, but he wouldn't sleep a full night. What kind of dim light are you referring to? Is there a lightbulb on? Do you mean they are sleeping into the morning when the sun comes up before their cage lights come on? If there's a light on at night, they won't be able to sleep properly, and that will also lead to issues. Also, was your male ever tested for parasites before you placed the female in the same cage as him? If not, you will want to have her tested, because he could have passed something onto her which is harmful. Finally, if you had given him too much water, either he would have thrown it up, or he could have aspirated from it going down his windpipe, but it doesn't sound like either thing happened.
I hope you are able to find some answers, and I'm just writing what comes to mind from your posts. Ultimately the vet can perform the necropsy, but my bet is that if it was the overdose of antibiotics or stress you won't find that out as an answer. I wish you luck, and hope that your female lives a long and healthy life.