Diablo – Killing resurrected monsters

In cooperative play, separate tickers happen for each party member, but you don't need to have a killing blow in order to benefit.

Massacre- This bonus counts how many monsters died during one unbroken chain of your attacks. As long as you are damaging monsters constantly, with pauses of no more than 1 second, you will continue to stack the bonus. When your attacks stop connecting with monsters for about a second, the system rewards you for all the monsters you wounded, that are currently dead.

Mighty Blow- the system counts how many monsters you wounded with one attack, that happen to be dead in the following second.

Destruction- I don't think it's possible for 2 people to simultaneously damage a barrel, since they go down in 1 hit. So, no sharing this one.

You do not lose the items; instead, they appear on the closest accessible location from where the monster is. So in your case, they will drop on the path right next to the monster. It will include the "drop" animation, so they will appear as if dropped from mid-air.

I've seen it happen a lot with flying creatures that were even further away from an accessible location than in your above screenshot, and I got their loot just fine. Fire away!