Based on the wiki (from the Kyle Shanahan and San Francisco 49ers pages), Shanahan's July 14 car accident left him with a severe concussion, fractured ribs, a broken hand, 40+ facial stitches, and a broken nose. Because the concussion recovery timeline is 1–3+ months, and assistant head coach Chris Foerster has taken over all on-field duties during training camp, it's very unlikely Shanahan will coach preseason games.
The team is being extremely cautious — Shanahan is limited to about 45 minutes watching practice before medical staff pull him off the field. The wiki doesn't give a specific return date for preseason action, but with the concussion protocol and the team prioritizing his health, Foerster is expected to handle all head-coaching duties through the preseason and potentially into the regular season.
Just a heads-up — the wiki calls it a car accident, not an "autopilot accident." No mention of self-driving or autopilot tech in the reporting covered there.