The Casting of Frank Stone requires you to make life or death choices about other characters, determining their fate. One of those characters is Stan, a mysterious individual you'll meet at Augustine Lieber's manor. As you play the game, you, Stan, and others will face various perils putting you in danger. So can you save Stan, or will he die no matter what?
The Casting Of Frank Stone: How To Save Stan
Unfortunately, there's no way to keep Stan alive throughout the entirety of The Casting of Frank Stone. You don't need to keep him alive to get the achievement for keeping all characters alive - Entity Displeased - since this achievement only requires you to keep all playable characters alive. At no point do you play Stan. Bonnie suffers a similar fate - you don't play her, so there's no requirement to keep her alive, and no way to do so.
However, when Stan dies is pivotal to keeping other characters alive, so this is still something that you'll want to pay lots of attention to. Your goal is to keep Stan alive whenever a quick-time event threatens his life. When he's threatened by Frank Stone and you get a skill check, for example, you'll want to make sure to hit it in order to get the best ending. (This isn't the case for Bonnie, who isn't faced with any life-or-death situations before her demise.)
When Stan eventually dies in every timeline, though, there's no way of stopping it. There are several ways he can die, but you'll know it's time if you aren't faced with any skill checks - you'll have to watch the cutscene and then move on with the story.
Stan unfortunately doesn't make it in any full playthrough of The Casting of Frank Stone, but that doesn't mean his death doesn't matter - you need to keep him alive for as long as possible to ensure the fates of other characters. If you want to get the Entity Displeased achievement, you won't need to try to keep Stan alive the whole time - but you'll need to succeed at QTEs determining his fate along the way to keep him from dying too early.