A friend of mine has a juniperus bonsai similar to this, but it is not doing well recently.

I noticed its top roots are now outside of soil, which I find not good, and I am about to suggest my friend adding a thin layer of a good substrate to cover exposed roots. But I am not a bonsai expert, so I am asking you - am I right?

There seems to be some fungi present on roots as well.

Update: Photos: