We have a practice at my program of utilizing a nurse as a tail guard for every landing. During scene calls, they clear the tail and then designate someone (police, fire, etc.) to take over tail watch. At hospital helipads, the RN always provides tail watch in all but very rare circumstances (Pt. actively coding in the back, etc.)
I would like to think that these practices could have averted this incident, though we all know how nothing is 100% and accidents will happen ( i make that statement with grain of salt however. i think that we can have an accident free industry, we just have to employ safe practices and maintain vigilance.). I would like to think though that most programs practice a tail watch/guard in their daily operations. If not, its something to think about. Even just having a nurse yell and motion to remain clear or retreat is usually sufficient when an incident such as this appears imminent.