Did the Scream kill off adepts and arcanists as well as psychics?
If space magic is a different application of psychic metadimensional energies, I'd say yes.
Or maybe there weren't any adepts or arcanists before the Scream? 🤔
In some sectors, there weren't any yet.
In other sectors, there are a bunch of 600-year-old ruins, relics, and Shadows created by Crazed wizards before they died.
Your GM's mileage can vary accordingly, if magic exists in your campaign at all.
Given the sneak peaks we've been given from the Codex of the Black Sun it seems the answer would also depend on which classes/organizations you include in your campaign. It would seem that utilizing the Godhunters as is would mean that magic existed prior to the Scream.
I certainly want to have space maɡic in my SWON campaiɡn as it fits tɡe character of the Aradian Leaɡue, an interstellar maɡocracy, much better than vanilla psionics.