As of now, there aren't any plans to continue the series. Director Susanne Bier told Oprah Magazine (via Oprah Daily), "Of course you wonder what comes after this is over. We did joke about it on set. I won't rule it out. But it's not in the concrete works." Further, in another interview with Marie Claire, she expressed her enthusiasm, stating, "I would love for David [Kelley] to write a Season 2."
Not only was "The Undoing" advertised as a "limited series" (via HBO); it's also based on a novel that doesn't have a sequel. However, as we know from "Big Little Lies," which also didn't have a sequel novel and was intended as a miniseries, that doesn't mean that a second season won't happen. The author, Liane Moriarty, even wrote a follow-up novella solely for those at HBO to use as source material for the next season (via Newsweek).
Additionally, Kidman was a major advocate of continuing the story. At a panel, as reported by BuzzFeed, Kidman said, "I had a lot of people say to me, 'No no no, that's it. You did only one. It was fantastic as one season.' And a friend of mine, a male, said, 'Those women deserve their stories to be told beyond what was just that first season ... Now you actually get to go and explore them on a deeper level and see the consequences and see their lives unfold in a much deeper way and that's what was so exciting for me."
It doesn't seem far-fetched that Kidman would feel the same way about "The Undoing." After all, there would be much to explore in the aftermath of the murderer being caught, especially for Kidman's character Grace. We'll just have to wait and see what HBO decides.
