Would Mr. Schmitz make appearance in movie version?
https://www.youtube.com/watch?v=RVs-W_hOPEU
No. Nor would it make sense it had anything to do with GUN given movie GUN was formed not long after the events of Sonic's first movie.
Unlike the upcoming Mario movie which seems to be all in with accurate representation of the games, Sonic movies are a loose adaption. I imagine Shadow's story will be similar to his story in
Sonic Adventure 2 but I doubt we'll get City Escape, Prison Island or Space Colony ARK.
My movie guesses the closest we'll get is:
City Escape = San Francisco
Prison Island = Alcatraz Island
Space Colony AR = Instead of space, it be either an underground research facility and colony similar to Fallout
vaults or, if it is a space colony, not without budget. I imagine Prof. Gerald Robotnik found it cheaper to build an asteroid colony on an existing rock than a full-scale space station, or the
International Space Station would be the movies take on ARK instead.
As for who killed Maria, well if the movie wants to go with the
Sega Cinematic Universe approach and choose another government agency to take the blame, or just generic MP soldiers and that's that.