90% Bird, 100% of the Time

There's a lot of debate on whether Akutagawa was truly dead or not before being turned by Stoker. We've seen him and various other characters survive grave injuries without mystical intervention (ie. Yosano), so it's not totally out of the question that he was still technically living at the time. Fictional works with vampires vary tremendously, however when it comes to mythology and legend it tends to be the case that vampires come from the dead. Because of that I believe he did legitimately die, but there's plenty of opportunities for that to change based on BSD lore. Considering we see Gin change over almost instantaneously after Higuchi's attack, it's hard to say that there's time for death to occur before turning, so that process could function differently from being changed via the main source (Stoker in this case).

All the same I'm not entirely shocked over the possibility that Akutagawa will be dead by the end of the series. Before everything became revealed, I was concerned over his respiratory health plus the fact that real life Akutagawa eventually killed himself. Once it was hinted that he would parallel Oda in a way, I felt even less confident that he would make it. We've seen evidence of Akutagawa changing and growing as early as ep. 11 with Higuchi's rescue when he steps up and apologizes to her, and from that point his treatment towards her seems improved/he's not physically or verbally assaulting her anymore. The changes continue as he cooperates with and acts as defense for Atsushi and gives his support to Kyoka in redirecting her path to a meaningful life. Even at times where he's fighting back against Atsushi, he makes statements towards the good Atsushi has in his life and tells him that his past in the orphanage being abused and ridiculed doesn't define who he is today.

We did see a genuine smile from him before going down, so perhaps he does feel enough at ease by saving Atsushi and therefore fulfilling something meaningful to his dedication to Dazai and drive to make him proud, not to say Dazai is the only basis in this action (we likely wouldn't see him smiling if that was the case). Rather than lose them both by not acting, Akutagawa could get Atsushi out of danger to regroup and continue the fight. I've seen others note how his keeping the promise to not kill by just knocking out the man attacking them in the ship led to Fukuchi getting distracted catching up with him and others, allowing Atsushi to properly escape without being tailed. We see in their tremendous capabilities combining Rashomon and Beast Beneath the Moonlight as well as in the cafe scene in the Beast AU that Atsushi and Akutagawa are kindred souls, yin and yang (their hair colors being the most obvious symbolism). In circumstances that do not automatically have them pitted against each other, they laugh and relate to each other, and I feel with that continued freedom they would become incredibly close and be a major source of healing old wounds together.

If inevitably he isn't revived, I think Asagiri will give us a meaningful last scene for Akutagawa. Asagiri has a wonderful way with writing deeply emotional, meaningful scenes, such as Dazai's response to Atsushi over the death of the orphanage director, and in a very major character death I'm confident we'd get the same efforts. Akutagawa's certainly done a lot of evil and destruction in his life yet in the end acted in unity and for the greater good, not just to prove himself or please Dazai. It would be late, but I have a lot of hope on the idea that Dazai would act very symbolically on the matter. Make sure he was laid to rest somewhere meaningful maybe? Hell I go as far to consider that when this arc is over that Dazai may finally commit suicide following Akutagawa's death, just as real life Dazai had, though in this case it being more of Dazai feeling that he did his part in becoming good, saving the innocent while combating evil, and forgoing his past rather than as an act of grief. Dazai creates a lot of humor surrounding his mental illness, but it is a major point to his character pulled directly from the real Dazai. Once again referring to the Beast AU, he follows through with committing suicide once he has done his part in the universe to bring Atsushi and Akutagawa together and to give Oda the chance to live peacefully, even if it means losing his friendship.