Your questions are excellent as I also hear about the story of Job but I have never really heard anyone mention what about his kids. I thought about this a lot in the past, and here is the best answer I can give right now. Of course, Job got restored, the kids did not. The kids in this case were part of Job's test. Without their death, the test could not occur. The test was so important that God would even allow death. So how is this just, because we know God is just? My conclusion is that the kids received their full reward. I would go so far as to suggest that assuming they were believers, that whatever they would have accomplished in their life for God, was given to them. So eternally, they are made whole, maybe even compensated with extra rewards.
I am somewhat undecided about the cause of all deaths. Some seem natural. For instance, the genetic code put that person at risk even before they were born. Other deaths are more a direct accomplishment of Satan. Many likely did not have to occur, but Satan tries to take advantage of every situation as he kills, steals and destroys. Still, the question remains: Could some contemporary deaths be a part of testing people that are still alive? I think so but it probably is rare. Of course, it is Satan doing this, and from God's perspective, He can make both those left living and those who died whole. So to me this is just, though it may not feel like it as most of us place so much more on living in this mortal body that we don't always look at the eternal picture.
I came up with this somewhat loose interpretation, after contemplating two very public ministries that were taken away. One minister died, and the other became incapacitated. Both are well known and preached healing and faith. So how come they had bad things happen? Testing is the only reason I could come up with. Their followers have to overcome, as these ministers became the test. I know some will question this interpretation, and say that perhaps they had a lack of faith or some reason that was not public. Possibly, but again, maybe they became like Job's kids. Only in these cases their loss tested thousands of people. In fact, all of us will hear or experience someone close to us dying so in a sense we all are tested in our reaction. Are we bitter toward God or do we continue to serve Him as a result of these deaths? Like Job we do have a promise of restoration. No one else's death has to impede what we will do for God or what we will receive from Him. And again, the one dying certainly could and likely is made whole by God in eternity.
