Hemsky looked to me like he left his feet prior to making contact. That is actually a good example of a clearly-defined rule that the NHL implemented a long time ago.
You have not yet suggested a rule they could implement that would reduce head shots to your satisfaction.
I will say this for the third time and then I'm done. When you have 200 pound players skating at full speed and expected to smash into each other, it's not reasonable to hold them to a standard whereby contact to the head is never made. Players should try not to make contact, but miscalculations will always occur that lead to accidental hits to the head. Unless you outlaw hitting outright.
True you cannot "stop" hits to the head for the reasons that you've given, but I do believe stricter measures can be taken that would reduce the number of cases further without eliminating hitting altogether. CHL for example applies a "no contact to the head" standard on all hits. Primary point of contact is not the basis of determining a transgression but simply whether the head was hit or not. Now I don't have the numbers for number of head related injuries in jr vs NHL so I can't speak to the efficacy of the standard, but I like the message and tone that it sets regarding player safety as a priority. And when last I checked, body checking was still very much alive and well in that league.
A similar to the blanket approach taken with high sticking years ago. Intentional or not, a high stick is called 100% of the time (*that the referee see's it). That approach puts the onus on the player to be completely responsible for their stick in all situations, even when being tripped or falling down. Now this may seem u fair or too hard too police yet I would say that, anecdotally at least, stick infractions do seem less frequent than I recall in the 80's and 90's (*eye test only). I think something similar could be applied here which would put clear onus on the hitter to ensure the hits they deliver are in situations where they have control of their hits.
Anyway it's probably only a matter of time for the league anyway, as the pending player's lawsuit is likely going to continue to pressure the league to clean up its rule book with regards to fighting and hitting lest it appear negligent in the court of public opinion.