@wayoung If Warner Media says that they're happy with how Dune Part 1 performs on HBO Max and want to greenlight/commission Part 2, I very seriously doubt that Legendary Pictures is going to say "No".
They will if their investors refuse to fund it which happened with the Kelvinverse films.
Or if the company buying them doesn't want a sequel on their books if the first one takes a loss.
Or if the incoming exec teams for either WB or Legendary don't want it for whatever petty reasons (like what killed the last, hugely successful, Dune TV franchise).
There's a lot of factors here. And the best way to jump past most of them was a monster box office. That didn't happen.
I think the best sign will be if The Sisterhood leaves development hell. Pre production on it froze while they waited for the movies results. If it starts up again, then everyone involved is happy enough to risk more money, and future exec teams may be stuck with continuing it as scrapping it means no return on invested funds.