At Monaco, the round following Imola, Karl Vendlinger had a hefty shunt which resulted in head injuries serious enough to require him being put into an induced Coma, despite the Sauber having quite substantial side head protection built in from day one.
The following season at the Australian GP Mika Hakkinen suffered a similar side to side head injury with almost as severe consequences.
Neither would have been protected by the Halo.
Just picking a couple if incidents at random: Jeff Krosnof (?) and Greg Moore were killed in CART rounds and the Halo would not have saved them.
Le Mans 1995???
Bloody ridiculous comparison.