Many shonen manga fans are sick of seeing character deaths reversed. Characters are regularly put in situations where they should die but miraculously survive. If they've suffered fatal injuries, it feels much more contrived. Manga creators can't help but hope for a happy ending.
In light of this, Endeavor and Dabi now having a way out of their apparent imminent deaths in My Hero Academia seems like it should annoy a lot of fans, but somehow doesn't. In another series, Rei's intervention in Chapter 387, "Congealing," would be seen as poor writing because it denied readers a well set-up death. Nonetheless, the context of this intervention makes it not just acceptable, but even welcomed. Because of everything it brings to the table, this specific near escape is narratively fulfilling.
Is Rei's Saving Endeavor and Dabi a Good or a Bad Thing?
On the surface, it appears like Endeavor and Dabi dying would make sense for the plot – and not just because of their grave injuries. Endeavor has been trying to atone for all of the abuse he's perpetrated on his family over the years, even though he'll never be completely redeemed. In the meantime, Dabi has been killing himself with his own tremendous firepower. Ending the story by having Endeavor sacrifice himself to get Dabi safely away from everyone who would otherwise be in his explosion radius could be a perfect ending for both of their stories. It would eliminate the two main reasons of the Todoroki family tragedy, allowing the remainder of the family to move on.
However, the possibility of Endeavor and Dabi being spared by Rei adds a few extra wrinkles to the plot. For starters, it places Endeavor and Dabi's fate in the hands of the entire Todoroki family, where it belongs. In reality, Endeavor is the only one who believes it is appropriate to remove himself. The rest of his family believes that it is critical for the entire family to work together to create a brighter future for themselves, which includes not only Endeavor, but also Dabi. Both of these difficult characters must live on in order to adequately atone for their errors.
Rei's rescue of Endeavor and Dabi also provides a satisfactory conclusion to the arc of a character who has been a powerless victim for the most of the story. It also reinforces MHA's overall theme of bystanders taking action to make a difference in the world. Rei may be a citizen, but she still has a lot of power in this position. It's extremely amazing to see her finally recognize and act on this, despite everything she's been through.
While Horikoshi's decision to leave Endeavor and Dabi's death may appear generic at first, Endeavor going the self-sacrifice way would be much more so. The fact that they were saved fits the story better and reinforces its themes and ideas. Even if the public doesn't think Endeavor or Dabi deserve a second opportunity, the decision is ultimately up to the individuals they've wounded the most.