I really really really don't want make one of those "You all would be mad if this was a Republican" posts, but seriously, if this was in the Bush Administration, Dems would (rightfully) be calling for heads to roll.
I agree with this sentiment, but if there is no hard drive left, we might as well stop caring about whatever wrongdoing Lois Lerner did. In my opinion, it is pretty clear that this was a cover-up, but genuine evidence is required to find anyone guilty of anything. Without evidence, I don't think that it would be acceptable to stick anything to Lerner and/or the others in the Obama Administration.
So, if a cop accused of a police brutality decided to destroy (sorry, "lose") the evidence, the accusation should just be dismissed.
Well, to get a guilty verdict from a court, you need to prove the offense.
In the case you propose, the logical answer is prosecuting the cop for destroying evidence.