Let's try to get an order of the probability... Let's say the parts land on earth with an an angle of more than 45 degrees. I'd take 1 sqm for each human, understanding the angle would reduce that number. Which makes around 10000 sqkm, counted generously. The earth total surface is around 510 millions sqkm. So that's one in 51000 chances for any human to be hit (calculated high). So quite makes sense that no one was impacted yet, but this seems not impossible as well - of course depending on how many satellites impact earth each year. Not counting that people are often in buildings, but one impact could kill more than 1, etc. Personally, I take this number for negligeable still. It would rather be hard finding anything build by humans killing less people.