I don't understand why everyone is talking about Bianchi. The Halo is not intended to prevent, or mittigate accidents like that. There's basically nothing that can be done to solve that kind of accident save from not putting 5 ton cranes on a live track.
The goal of the halo is to protect against accidents like Massa's, Willson's and Wheldon's, where the driver is struck on the head by a substantial object.