Good idea..for huge caves. I've been caving for 30+ years and I can tell you that a skilled and well equipped human will be able to explore more than one of these airships. Sometimes passages are obstructed by ceiling collapses. ( after water drains from the cave due to the lowering of the base level rock will fall off the ceiling due to the loss in buoyancy). Sometimes one needs to move a few rocks to get by. Sometimes you just need to squeeze and contort to get through. Sometimes you need you dig a bit of sediment because it fills a passage to the point of preventing preventing access.
Having said all that, the one time when this would be helpful is when you enter a space with an extremely high ceiling. One can bolt up the wall see see what's there. But the better/easier way is to use a drone to do recon first.
My caving experience is less than yours, but I want to echo what you say. The average person envisions spacious tourist caves, not belly-crawling 800 yards through muddy gravel which has been more my experience with wild caves in the American Midwest. Gear gets shredded in caves worse than maybe any other environment, and slows you down like nothing else.
There was a recent David Attenborough narrated documentary about a huge cave system in I want to say Vietnam. In the behind the scenes making of short they said drones would not work underground due to some built in programmed restrictions. They had to contact the manufacturer to get the firmware changed to allow it.
That applies to commercial drones. This one has selfmade flight control electronics. 'Selfmade' as in using common of the shelf electronic components, not something locked down like from DJI fi.
The setup is described in the paper if you scroll down. (Experimental) Html-View in the upper right working perfectly without having to download it.
Having said all that, the one time when this would be helpful is when you enter a space with an extremely high ceiling. One can bolt up the wall see see what's there. But the better/easier way is to use a drone to do recon first.