no, someone said in the comments it's part of their plan
Nah it's more likely that Keith made a deal with the warden. I got the vibes that the warden was annoyed with Della but also thankful bc he got all the prisoners to listen or something. So he wouldn't have a reason to kill him. But Henry does want to kill Robere, so even if Della left the prison, he'd still be at risk. Pronouncing him dead would stop the prosecution and also get Della out of prison, which would be a win for the warden and a win for Keith since he fell in love (probably) and wants Robere to live.
Knowing the way these things normally go, Keith probably arranged things so that Robere/Della can go freely live his life and Keith is stuck with Henry. Not because he loves him but bc he views it as some sorta atonement for his past actions or some bullshit. Also to keep an eye on Henry, so that he won't get the idea of looking for Robere again.
That's my speculation based on how the story went so far and how these stories usually go, sprinkled with a bit of what I personally would write.
What? He fawking what????? IF HE'S FXKING DEAD THEN THIS MANHWA IS DEAD. Nobody wanted della dead like btch pls?? Or should i just calm down cuz there's plot twist- like, henry helped della escaped or whatsoever?????