This is very strange.
Did you remove the TeslaCam drive from the car and look in the RecentClips folder? The most recent hour of video should be in there. The next step is to use an undelete or file recovery program to find all the erased files on the drive.
I cannot imagine how the crash would cause the entire day's video from before the crash (and nothing else) to go missing. Do you remember if the dashcam was working on the day of the crash? I think there is a red dot on the icon on the touchscreen when it's recording.
The dashcam USB storage devices can malfunction and stop recording even if files can still be read from them. If video from that day is not on the drive, my guess is the drive stopped recording that day or was accidentally turned off. I realize this is unlikely and unlucky but I don't think it's possible for a crash to cause videos from that one day to disappear. Newer files are not more fragile than older ones.