If they kill Iron Man I will be in shock. The 3 Iron Man movies (even with 2 sucking and 3 being OK) have grossed over 2.4 Billion dollars. RDJ is the straw that stirs Marvel's drink, more so than any other character or franchise.
My prediction is that IF a major character is killed in Civil War they will probably be brought back to life at the end of Infinity War Part 1.
"Fairy tales do not tell children that dragons exist. Children already know that dragons exist. Fairy tales tell children that dragons can be killed."
-G. K. Chesterton