So, according to Zeno, in order to break the Crimson Dragon King and the Four Dragons cycle, one must first use the chalice to absorb white, blue, and green dragons essence/soul. Then use the shield of the Crimson Dragon King to open the path to his resting place and take his sword and use said sword to pierce the yellow dragon and let his blood fill the chalice (in which his essence would also now lie). All of which must be done within day or at least before dawn rises, otherwise it'll apparently fail (probably since the other dragon's essences would escape and either return to human form or reincarnate in new individuals.
With that said, I don't think Zeno's plan would work (at least not to what he expects), mostly since The Crimson Dragon, Yona, still lives. Now before Yona's birth, this ritual might work, since the Crimson Dragon's spirit hadn't reincarnated yet, and completing the ritual would mean that all of the Dragon spirits would return to the heavens, and the cycle would truly end. Now I know Zeno just said that Yona and the Crimson Dragon King are two different individuals, however I don't think that matters much since she still carries the soul, and we've seen throughout the series that Yona's soul is reactive force for the Four Dragons (they can sense each other, and when Yona's in danger, their strength greatly increases in response to save her).
So, since Yona's still alive, I wouldn't be surprise that Zeno will rapidly heal (since he's close to the castle, his healing speed increases), and of course he'll be confused before coming to the realization that he has to kill Yona before he can end the cycle, and that will lead to his confrontation with Hak that Yona had dreamt about.
With all that said, this was definitely a heart wrenching chapter, and I kept hoping that near the end that someone will grab Zeno before he stabbed himself. Also, glad to see that Lili's doing well. Her interaction with Zeno was a brief and blissful moment. Looking forward to the next chapter.