You can also try saving the footage to a USB drive as long as it's formatted as FAT32 or Ext2/3, that might provide you with another mechanism to save the footage if something has gone awry with the SD card slot. To know more about why the SD card was not being detected correctly, we would have log into the camera via to SSH (using the micro-USB port) and check into what the kernel thinks of the SD card. If you can manually mount the SD card using the Linux mount command then the UI should still be able to save footage to it.
If you're on one of the 0.3.1 software releases, and you have SSH access to the camera, then you can also use the /opt/camera/cam-recover tool to extract footage from a camera isn't able to save via the normal method (be warned that this option is quite slow).