The results depend on what the spherical objects are made of.
Assuming stone, I don't think anyone dies. The D guy would die if he doesn't move, but that's stupid - all he needs to do is bend his knees and he's fine. So, he's fine.
The C guy is fine too. Because the see-saw has a heavier ball on the left side, holding it down. The momentum of the rolling stone would give it a lot of horizontal power, not vertical dropping power when it hits the see-saw, so the see-saw would not be pushed down on the right. Unless the see-saw is made of a weak substance, in which case the stone ball could break it, and C guy dies. But I'm assuming it's strong.
The only potential casualty would be B, if the rolling ball had enough momentum to roll over the stationary ball. But if these are made of solid stone - it's not going to happen. It's too heavy to hop the stationary ball. If these balls were made of wood - it might hop the ball, and crush the B guy. If the ball was made of 400 pounds of latex, then it will probably take out B and A!
Also, the crescent doesn't do much, other than slow the ball down a bit. The gap of the crescent does not create a "miss" for the D guy.