In the Marvel Comics universe, death is more than the state of dying. Death is a cosmic being that could be older than the universe itself. She doesn’t decide who dies. She’s only in charge of it.
Since Death has never been mortal, she’s never known what it’s like to feel their emotions. When the mother of a young girl named Christine Collins found her way to the afterlife (Thanos No. 3 by Christopher Cantwell), she asked for her daughter Marie’s life back. Death refuses her request. After being denied, Christine called Death a coward. Christine said she was going to beg, but then said she felt sorry for Death. This leads to Death going to the Illuminati (Tony Stark, Reed Richards, Dr. Strange, Adam Brashear, and Emma Frost).
Death tells the Illuminati that she wants a human life and death (she chooses to look like Marie). Since she has the power, Dr. Strange suggests she does it herself. Death explains it would upset a larger balance and make her siblings curious (there's no way this is the last we hear of her siblings this year). Smartly, Tony sees an opportunity.
Tony and Emma Frost suggest a quid pro quo. Death makes an offer they can't refuse. She says, "The...extinction of your world will occur sooner than you think. In your lifetimes, in fact." All they have to do is accept her request and protect her. After that, the Infinity Well will call and answer their questions.
The next Marvel Comics crossover is Blood Hunt (you can see the trailer above for more). During this event, it looks like the sun will be blacked out all over the world. Without daylight, the vampires will have an advantage they've never had. They can feed and fight without a time restriction. It’s easy to think that this is the extinction-level event Death is referring to, but this writer doubts it.
Vampires on the hunt is a terrifying thought. However, it’s not an event that can destroy the world. Whatever Death knows is bigger than that. In the upcoming months (maybe weeks), Marvel should announce something huge. Don't be shocked when the Infinity Well calls the Illuminati in Thanos No. 4.
Stay tuned to Bam Smack Pow to find out what's next for Death, the Illuminati, and Marvel Comics in general.