I'm just wondering, in the episode where Hidan lost his head against the Konoha jounin, which he killed eventually (forgot the name). There is a scene where he lost his head, and his body is still moving, looking for the head. Until Kakuzu stitched Hidan's head to his body. Then in the scene where Shikamaru buried him, Hidan is literally disconnected with his body (or did some of his parts even get vaporized?) But his head is still working. Supposing his body parts could still move on its own regardless if they are not connected with a central nervous system, could Hidan "chew", "claw", "divide" his way out of the hole? and then from some bit make himself whole again? His becoming whole again would incur maybe centuries, lets just say that somehow his tissues would become whole again over time. The topic would be, if he could get out of the mound which Shikamaru created from him.
It is impossible for Hidan to crawl out of his hole.
- His body was destroyed. When he was captured by Shikamaru, his body was exploded using exploding tags, leaving only his head. So, having his body digging the hole would be impossible.
- While Hidan is immortal, he doesn't seems to possess healing ability. This is proofed by the fact that he needs Kakuzu to stitch his head back to his body. He can't do this himself by means of regeneration. So, it'd be impossible for him to regenerate his already lost body and have it dig for him.
- He was buried several meters underground. It wasn't said how many meters but from the image shown in the manga and the anime, I'd say it is about 3 meters or more with the diameter approximately 1 meter. So using the formula for tube volume, pi x r x r x h, we get 3.14 x 0.5 x 0.5 x 3, which is 2.356 meter cubic of soil. 1 meter cubic of soil is about 1,200 kg, so that means he have 2,827.433 kg of soil weighing his head.
- Digging from inside is an impossible task. When digging from outside, you move the mass from one place to another. However, since his head is surrounded by soil, suppose that he use his mouth to try digging, he would not have place to put the soil away, not to mention that when he do so, the soil above would fall down. His option would be to swallow it, but I doubt he would be able to swallow 2,800 kg of soil and then using his mouth to climb out of the hole.
- Hidan is buried in a forest belonging to the Nara clan. Suppose that somehow he managed to climb his way up, as implied by Shikamaru when he buried Hidan, the deer in that forest would contact the Nara clan and someone would send his head back into the hole and bury him again.
- He can't wait for centuries. Naruto Second Fanbook stated that while Hidan is indeed still alive, he is dying from malnutrition.