That's not how liability works. It's not a hot potato that stops with the first person in a chain of people who did wrong. Everyone who contributes to a catastrophe of broken rules essentially gets a slice of the consequence pie the only thing that changes is how big a slice of the overall pie you get.

Here's what the situation says to me. You have a 1st AD and a Principle and senior Actor/ Producer who were breaking the most basic of rules. For context on a film set say a camera person sets a case of lenses on something I as a set dresser need to move. It is largely unacceptable for me to even touch that box until I have tried everything viable to hail the correct department to move it. If somebody tries to hand me something I am not supposed to be handed I go talk to their supervisor. Some things even if I have explicit permission to handle from a props person, like a gun, I am liable if I handle it anyway because there is no circumstances where me putting my hand on that item is acceptable. First rule on a set you learn day one "Don't touch ANYTHING that belongs to someone outside your department".

If this incredibly basic rule was SO flagrantly violated on so many levels by THE CHEIF SAFETY OFFICER ON SET that tells me that the safety problems and the culture of improper protocol were endemic on the set. This very obviously wasn't one bad day of lax protocols. This was an unsafe set and an everyday unsafe crew culture. Lots of times you don't get burned when something isn't safe so people try their luck which is all fine and dandy until tragedy hits.

This AD had a previous incident where a gun he handled fired a live round went off on a set and just didn't hit anybody. At that point people should have fucking hung drawn and quarted him and busted him back down to Trainee. He was a demonstratilably consistent danger to the crews he was on but Rust STILL HIRED him as their primary safety officer anyway.

When something goes this desperately wrong that pie gets so big there's a slice for everyone. The other Producers on this show had a duty to hire people who do the job properly. The 1st AD is a major hire. Ist ADs arguably do more to protect production liability than a Director does and production has their eye on the pick. If something a director wants is unsafe it is a 1st AD who has veto power. They set the culture of the set to make provisions for safety. If you rent a peice of equipment that has a record of dangerously failure and one of your workers gets hurt by it you as an employer get burned. The same goes for personnel. The producers absolutely should find some liability pie on their plates too. Are they gunna get prison time? Probably not but they are still negligent and there are consequences that scale to fit.