I haven't watched or read Death Note, but I did look up the rules established by the series as I've also wondered about how clever one could be.
In the particular case of "A, B and C die in a fiery yacht explosion", if the yacht explosion would kill other people, they'd just die of heart attacks instead. If one of them was piloting the yacht and their death would cause the yacht to kill somebody else, they'll die of a heart attack at the soonest point after the scheduled time of death such that their death won't be the proximate cause of somebody else's death. (Can deaths caused by the Death Note cause collateral damage short of death? Maybe, but I suspect invoking them in the death condition would either result in those conditions being ignored, or the victim dying of a heart attack instead: it's a Death Note, not a Fractured Arm Note.)
(Pulling back from the billionaire example: a surgeon won't die in the middle of surgery if this would kill the patient, but it's permitted that somebody might die sooner as the result of the surgeon no longer being available to operate on them. Curiously, Shinigami will see the indirect victim's lifespan as it would have been had the surgeon not died.)
I feel that the rules on disease are illustrative of the limits of the Death Note:
"X will die of COVID in 10 days" will result in them contracting COVID and dying in 10 days.
"X will die of lung cancer in 10 days" will result in them dying of a heart attack in 10 days, unless they already have a case of lung cancer that could reasonably kill them.
"X will die of lung cancer" (with no time specified) will cause them to get a case of aggressive lung cancer, which will kill them as soon as it realistically can, even if that time is outside of the typical 23 day window the Death Note operates in.
There are also rules indicating that the conditions of death must be physically possible, and reasonably carried out by that human. This prevents deaths like "X explodes into a swarm of kittens" and "X dies while reentering Earth's atmosphere" (unless e.g. X is an astronaut).
While not explicitly stated, I suspect:
If you indicate that somebody is killed by a falling meteor, the Death Note will strive to get them into a position where a meteor of sufficient size was going to fall anyway. It's not going to violate conservation of mass to summon one into existence, nor conservation of energy to shove one towards Earth. If there's no viable meteor candidate reachable under normal circumstances: heart attack.
You might be able to specify another person as an agent of an accidental death, but you can't use the Death Note to force somebody to become a murderer unless they were already inclined to murder the victim: the Death Note will provide opportunity, but not motive or inclination. (This is heavily inferred from a rule stating that "all humans are thought to posses the potential to commit suicide".)
Expanding on the above, the fact that the Death Note can manipulate plausible accidents to happen indicates that it must be capable of influencing the behaviour of people other than the one listed in the Death Note, but I suspect that influence is minimal. Influence over the named victim is greater, but still has limits: nobody will hijack a plane just to make it to their appointed time and place of death.
On the feasibility of an "AI server farm explosion", you'd need a reasonable way for the server farm to explode (gas leak?), a means for the victim to be inside, and a high likelihood that nobody else is present at the time.
My recipe for causing chaos with a Death Note would be to have a lot of "accidental" deaths at the hands of various second-in-commands. Sure, pushing their boss down the stairs was an accident, but good luck convincing the rest of the world of that when they're the immediate beneficiary of their boss's death! This will help preemptively erode the power of the victim's replacement (also probably a shitty human being), and also sew paranoia amongst the victim's peers.
janainaart
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tangentwithtanner
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