Ouch!!
I wonder if the Bendix simply unscrewed, jammed into the nut and wore everything out and generating the FOD that got the compressor.
There is a chance that the leading edges of the turbine wheel also is damaged by that same fod on its way thru, but not visible from the rear
The fact that the bearing feel good is a good sign.

Stuff the K80 into the R54, We have a R54 at our field with a K80 in it.

I had to make a custom spanner wrench to tighten my Jet Cat bendix. The starter may be fine, you might just need a new bendix. The JetCat starter motor is very expensive for a $4 motor.