The fact that I Am Legend 2 is happening with Will Smith set to star alongside Michael B. Jordan means that the alternate ending of the first movie has to be canon. Taking many by surprise, a sequel to the 2007 film was announced despite more than a decade with no indication that the adaptation of Richard Matheson's novel would receive a follow-up. Instead, most expected a remake or TV show of I Am Legend. Despite the success of I Am Legend, which claimed $585 million at the worldwide box office, the film had a mixed reception and didn't seem sequel-friendly as the main character, Robert Neville, died at the end.
The main criticism leveled at France Lawrence's film was the fact that the ending was so different from the one in the books to the point that it completely missed the point of Richard Matheson's story. In the book, Robert Neville realizes moments before he is executed for his crimes against the Darkseekers that he was the monster for that new species. The legend in the title, therefore, referred to his role as a boogeyman rather than a survivor. I Am Legend, in turn, avoided Will Smith's character being perceived as a villain and went for a more Hollywood ending in which Neville sacrifices himself to destroy the monsters and save Anna and Ethan. There was, however, an alternate ending to I Am Legend much closer to the end of the novel.
In the alternate ending, Neville realizes that he had kidnapped someone important to one of the creatures and that his attempt to cure the Darkseekers was only bringing them pain. Neville lets that Darkseeker go, and leaves without any sort of confrontation with the creatures. In addition to working much better as an ending considering the story of the novel, the alternate ending to I Am Legend is also the only one that would allow a sequel with Will Smith returning to properly happen as it keeps Neville alive. I Am Legend's original ending sees Will Smith's character being blown up and becoming a legend to other survivors, while the alternate ending indicates that Neville will have to deal with the consequences of his actions and the implications of his discoveries about the true nature of the Darkseekers.
If Will Smith's role in I am Legend 2 was only expected as a cameo in some sort of flashback, however, then the official I Am Legend ending could work just fine. But that doesn't seem to be the case, as the actor is reportedly co-starring in the sequel alongside Jordan. If the alternate ending is truly regarded as canon over the released I Am Legend ending, then it means that those involved in the sequel will have realized that it was not only the best ending, period, but also the only one that makes Will Smith's return possible.
I Am Legend 2 finally happening with Will Smith's return is great, but it's impossible to be pulled off without the original movie's alternate ending, not its theatrical one, being the starting point for the sequel. Making that version canon to the original film more than 15 years later would be a historic decision in terms of Hollywood franchises and alternate cuts. More on Smith's return as Robert Neville, and how Jordan will factor into the new story, will be revealed once the production for I Am Legend 2 picks up.