I figured it out myself… I realized that the /dev/mmcblk0p2 is the whole OS root folder, and /dev/mmcblk0p1 is the boot CD folder when you plug the BBB on a computer. Also, I found that there are three folders in /media folder, and the third one “rootfl” is the folder of the eMMC!
So before doing anything further, I simply copied all the useful files from the eMMC to the boot CD folder, shut down, put the SD card back to the computer, and uploaded all the backed up files into my Google drive. Bam! Now I can play with the BBB without any concern..
Then I run the similar sentence referred from the webpage I linked in the last post as follows (of course run the “mkdir /mnt/microSD” and "mount /dev/mmcblk0p2 /mnt/microSD” first):
cp -r /mnt/microSD/lib/modules/3.8.13-bone/ /media/rootfl/lib/modules/
and shutdown, eject the SD card, boot, … It’s back to life again!