Manifest season 4 could bring back Danny as a result of Grace's death in the season 3 finale. After NBC canceled Manifest, fans began to worry that the cliffhanger ending to season 3 would never be resolved. The episode concluded with three huge surprises: Grace (Athena Karkanis) dying after being stabbed by Angelina (Holly Taylor), Angelina kidnapping Grace's youngest child Eden, and Cal (Ty Doran) returning as a much older version of himself.
The future of Manifest was saved by Netflix after the show continued to perform extraordinarily well on the streaming service. Netflix renewed Manifest for a fourth and final season, which will consist of 20 episodes that might be released in two parts. This will allow the series to reach the ultimate conclusion the creators wanted, albeit a bit faster, and allow season 3's cliffhangers to be resolved. Much of the cast is returning to help wrap up Manifest's story and that could include the return of Daniel Sunjata as Danny.
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Manifest introduced Danny early on in season 1 as the romantic partner Grace found during the five and a half years her husband Ben Stone (Josh Dallas) and the rest of Flight 828 was missing. However, Danny exited the show at the beginning of season 2 after it was determined that he was not the father of Grace's baby. Manifest didn't make any effort to include Danny after that or mention his involvement in the family's past. But Manifest has shown that any character could return down the road in surprising ways, so Danny could be the latest familiar face to appear in Manifest season 4. This might have already been set up as a result of Grace's death and Eden's kidnapping.
Grace's death is a natural way for Danny to resurface in Manifest season 4. He loved her for several years and grew close to Olive (Luna Blaise) during this time. Grace's death will send shockwaves through the Stone family and it would be understandable if that leads to Danny re-entering the picture. At the very least, Danny's return could happen during Grace's funeral as he should be allowed to pay his respects. Danny could also take on a bigger role in the season by being the one who Olive reaches out to as she tries to grapple with the death of Grace.
There's also the chance that Danny's return in Manifest season 4 could be less helpful and more problematic. There's no knowledge of what Danny has been up to during the last few years, but it wouldn't be too surprising if he quietly developed some animosity for 828 passengers. Grace's death and the kidnapping of Eden at the hand of Angelina could make him become anti-828 and view them as a problem. His anger towards the passengers and what happened to Grace could lead him to be a wildcard in Manifest season 4 and doing whatever it takes to avenge Grace's death.