Yaw/roll divergence hasn't come up yet. It was demonstrated once to me at height - the ac lost height very quickly. I believe an RAF Puma was lost in France due to YRD in the seventies.
The Puma yaw/collective interlink seems to do the job quite well. How grossly does one have to fly out of balance to induce yaw/roll divergence? Can it catch one out after an unintentional brief but harsh application of sideslip?