One way to check if scheduled flights are disappearing is to do a compare of flight availability for booking to the flight schedule page at
https://www.alaskaair.com/schedule/.
A quick check of BLI-SEA, flown by Horizon and SkyWest, finds the last flight of the day on Friday, Nov. 7 (4:04pm) is gone. The schedule shows 4x frequency BLI-SEA and SEA-BLI daily for the next couple of weeks. The booking engine only shows 3x now on Saturday.
Imperfect, but an indicator of what's likely to come this weekend.