I suspect that the delay is down to insurance. MoD employee takes instructions from Castle employee who publicly accepts culpability. The lawyers' fees and admin costs are going to greatly exceed any reconstruction costs.
Rebuilding a Listed wall is no slower than building an unlisted wall.
If someone writes me a formal instruction and provides photos of both sides of the wall as it was before the incident, I could arrange to have it back in service by Saturday. (A week on Saturday if any of the stone has to be replaced).