I think you should certainly allow them to finish their work, yet question what could happen if someone determined enough drilled through this unearthed metal capping. Though I cannot say if the capping must be earthed, I would certainly think it would be an improvement, and very easy to do at this stage. Each piece would need to be earthed.
But the question is, is this still going to be safe enough? It's certainly an improvement on before, and the damaged cable has been replaced. You know where the cables are, you have pictures, but no one else knows, and nobody has any way of tracing where they run.
I still claim the safest place for the cables is in the brick cavity as they would be hard to drill through. Last I heard, on this site, was that meter tails are the only cables allowed in a brick cavity. However, your people say otherwise.
I think Holmslaw's comments are very valid.