I had this happen when my chain broke (or to be more accurate, my chain's masterlink unplugged). The break occurred on the lower section of the chain, so the spring-loaded derailleur cage whipped the chain back. It coiled around the derailleur, and my own pedal stroke pulled the derailleur up and around. The RD was ripped in half, similarly to yours.

So my contribution to the forensics is that your skipping chain might've been a link in the process of breaking. If you have chain skipping occurring once with each pass of the chain, it's wise to STOP, LOOK, and LISTEN. Sight down the chain lengthwise from the rear and backpedal, it's relatively easy to spot twisted or half-broken links from an end-on view. Watch at the pulleys for a link that hops or doesn't swivel properly.