Yes, Marcus Mariota is expected to start multiple games for the Commanders. Here's the situation:
Jayden Daniels dislocated his left elbow on the final play of the first half in Week 2 at Dallas (Sept. 20). Ian Rapoport reported the injury mirrors Daniels' Week 9 2025 timeline, suggesting a 2-to-4 week absence at minimum (from the Marcus Mariota page).
There's a Sept. 22 news article titled "Multiple Marcus Mariota Starts Likely For Commanders; Jayden Daniels IR Stint Not..." — so it sounds like Washington could be cautious and hold Daniels out beyond the minimum, but may not go the IR route (which would cost him 4 games minimum).
On FantasyPros, they noted Mariota is "taking over for at least the next couple weeks," with real concern about what the offense looks like without Daniels under center.
Bottom line: You're looking at at least 2-4 starts for Mariota, possibly more depending on how the elbow heals and where the Commanders sit in the standings. He's a capable game manager (1,695 yards, 10 TDs in 8 starts for Washington in 2025), but not someone you'd want to start in standard fantasy leagues.