So many people are saying it wouldn't hit him without the Halo there. They all seem to ignore two major factors, one, Leclerc's car is as normal there, moving directly towards Alonso's car, it doesn't matter that it at one point was just ahead of him, Leclerc's motion is taking him in to it. Second and most important, the halo pushed Alonso's car forward (from Leclerc's perspective). As it hit the wishbone and the tire Leclerc's forward motion also mean the halo was moving forward and exerting force on Alonso's car, it pushed it forward in midair. Without the halo leclerc moves forward without something to push Alonso's car forward as it moves sideways and his head is going to end up much closer than it did and maybe enough to be caught by the tire.
So many people are treating it as if because the front (well actually back) part of Alonso's car passed infront of Leclerc, the front would have easily as well as if Leclerc's car wasn't moving towards it.
People's spatial reasoning and inability to see what effect the halo had on the movement of Alonso's car is insane to me.
I can't say for sure it would have hit Leclerc's helmet, but it would have been exceptionally close, much closer than the halo allowed.