Finding out exactly how much damage was done will be difficult to determine for a few days. The US said that caves were one of their targets, and frankly, what and who were in them, and how much destruction was delivered will take time.
For those who may be curious, a GBU-43 is a guided bomb, hence GBU, with an approximate weight of 22,600 lb. Approximately 18,700 of it is explosive filler. The bomb is detonated by proximity fuzing, that is, the fuze is programmed to function at a certain distance above the ground.
It is not a fragmentation bomb. The large amount of HE (high explosive) composition inside is designed to create a large pressure wave, which violently moves the air. The leading edge of the wave moving into a cave will cause the air inside to compress because there will not be adequate ventilation to allow the air to flow out. A poor analogy, but think of a pop can that you shake and then open. There is violent venting and you get covered in carbonated water.
The people inside will have their ears ruptured, body parts torn off, guts forced out and shaken apart. How much so depends on where they are in proximity to the blast. Although the MOAB is not a fragmentation bomb, this rapid, violent air movement will cause any debris, natural or man made, to be blown around, striking whoever or whatever is in the way.
The lucky ones will be the people standing exposed to the pressure wave as it travels outward. They'll basically be torn to atoms. The unfortunate ones will be the ones who are too far away to be killed instantly, but encounter the blast wave or frag flying around in the air.
Apart from its size, this is a conventional HE bomb. Besides satellite imagery and fly overs, the only way to fully assess the damage is for people to go in and look around. It will be interesting to read about this part of the operation. They will want to itemize equipment and personnel losses not only to complete the after action report, but to discover how effective the MOAB was on its first deployment.
You can read a little about the GBU-43 here.
https://en.wikipedia.org/wiki/GBU-43...ance_Air_Blast (external - login to view)