Lets suppose, that the moon, was a Dyson sphere, and its power unit failed,
and its orbit began to decay, then it would hit the earth.

Then what would happen?

It would bounce a few times, and then finally contact the surface like two
cogwheels grinding the surface to a mushy pulp, and then finally
come to rest. Like two uneven barbells.

Yet we don't see any planets like that do we?