That was only the case for me when he was younger - like: could this little guy die easily?
(Didn't worry regarding escaping as I'm sure he cannot open the enclosure, opens from the top, tube lamp must be removed before opening.)
Nowadays, when he's not visible, I don't worry - when he's not visible, he is usually hidden in the cave you see in the photo, or in another cave that goes really deep down (he dug it out between the back wall and an aloe plant, and he brumated down there), or behind a thick branch. When I didn't saw him, I also didn't worry, just did a few things in the enclosure, refilled bugs... watered plants... thinking "so when he's coming back up later that day everything is nice"... and then I recognized he was sitting
right there, a centimeter from my hand or so and I hadn't recognized
Usually, when I open the enclosure and he's within reach, I touch him and he gets a bit of a cuddle (he then licks my hand) - I then did so promptly