Should we be concerned that it's been 3 hours with no word back from our dear friend?
Don't worry, the bat has not killed me.
...
Anyway: After I posted this yesterday, I kept the window open, turned out the light and closed the bathroom door so that the bat can fly out. After 15 minutes I looked in again and the bat seemed to have gone because I didn't spot it anymore.
Today, when I got back in the bat was still there and sleeping on one of my curtains.
I decided to put on some thicker working gloves, took it and put it out in the open. The bat seemed to be a bit perplexed because it wouldn't fly away (maybe it was still half asleep) and tried to bite and hiss like a cat. I decided to put it on a tree outside the house.