One last attempt.
The building starts to self-destruct.
Zack and Rachel make one last bid to escape as the facility collapses around them. With self-destruct activated, the entire facility springs into flames, which hinders Zack. Zack may act strong, but he hates lies and most of all fire, which is how he first got the horrific burns all over his body. In the end, it’s up to Rachel to continue their effort forward.
Danny… still isn’t somehow dead, and interferes yet again. At this point it’s hard to tell who’s more immortal, Zack who’s been nearly eviscerated, or Danny who’s been shot and nearly eviscerated. These people in this facility, really.
Danny’s last attempt at letting Rachel stay isn’t a surprising one- he turns his obsession into violence. He decides that if Rachel wants to leave, then he won’t let her, and shoots her. In Danny’s logic, Rachel dying in the facility is much more preferable to her leaving Danny’s control. After all, if he kills her, he robs her of her agency, her ability to choose to not pick him, and so she can remain his forever. It’s a similar mentality to how Rachel treats her corpses: in killing someone and reducing them to something that can’t act on its own, you can force whatever narrative you want on them- even if it’s a narrative contrary to how they acted while they were alive.
Of course, Rachel now doesn’t want to die. She’s been renewed with a new sense of vigor; it’s not just the fact that she did terrible things and must be judged, but she wants to die by her own terms. Now that she’s been shown something that’s not just her own desires and Danny’s desires, she has changed. She is not emotionless and hollow like we originally thought her to be. She has her own wants, and she wants is to get out of there with Zack.
Danny points out that if she dies, then she wouldn’t have fulfilled her promise. In a sense, this is true, since as I said, the dead have no agency. However, Rachel views it very differently. According to her, not even death can break her promise with Zack. After all, she tried her hardest and at this moment, is continuing to try and fulfill her promise. Even if she dies, she didn’t die to turn her back on Zack and everything that he did but continued to strive forward. As long as she doesn’t give up, then her promise holds true.