“They were noticeably absent from today’s press release from Marvel Studios that unveiled the main cast and characters returning or being introduced in Thor: Ragnarok, but you should still expect to see Lady Sif and the Warriors Three together again next year.
The four supporting characters played by Jaimie Alexander, Zachary Levi (Fandral), Ray Stevenson (Volstagg), and Tadanobu Asano (Hogun), respectively, are the most loyal of friends and battlefield allies to Thor. And when prodded about the absence of Sif in the Thor 3 cast announcement, Alexander immediately told her fans, “don’t worry.” So don’t.
It’s odd that if these characters were to return that they’d not be mentioned by Marvel but it’s not uncommon in Marvel press releases where for every single movie (including Doctor Strange most recently), certain supporting characters were confirmed later (in that case, Benedict Wong). It’s possible they’re being saved for another, separate announcement alongside more concept/character art.
Below is a key frame from Thor: Ragnarokthat coupled today’s news for instance – news that focused on the main returning characters, but even moreso on the four key additions (Cate Blanchett, Jeff Goldblum, Tessa Thompson, and Karl Urban)…”