no adb devices detected after failed revert to Android
Just did all the necessary steps on my N7:


Download the factory image from Google
Unpack the downloaded file (e.g. by tar -xvzf nakasi-jdq39-factory-c317339e.tgz)
Boot your N7 into the bootloader (hold the power and both volume buttons)
Have fastboot installed (comes with the SDK or for Ubuntu, just install android-tools-fastboot)
connect it to your machine
Flash it using flash-all.bat or flash-all.sh (needs installed fastboot)


Here's the transcript (using Ubuntu):

me@localhost:/tmp/nakasi-jdq39$ ls
bootloader-grouper-4.18.img  flash-all.sh   image-nakasi-jdq39.zip
flash-all.bat                flash-base.sh
me@localhost:/tmp/nakasi-jdq39$ bash flash-all.sh 
...
(bootloader) Bootloader is already unlocked
OKAY [  0.020s]
finished. total time: 0.020s
erasing 'boot'...
OKAY [  0.104s]
finished. total time: 0.104s
******** Did you mean to fastboot format this partition?
erasing 'cache'...
OKAY [  0.147s]
finished. total time: 0.147s
erasing 'recovery'...
OKAY [  0.106s]
finished. total time: 0.106s
******** Did you mean to fastboot format this partition?
erasing 'system'...
OKAY [  0.175s]
finished. total time: 0.175s
******** Did you mean to fastboot format this partition?
erasing 'userdata'...
OKAY [  1.401s]
finished. total time: 1.401s
sending 'bootloader' (2096 KB)...
OKAY [  0.286s]
writing 'bootloader'...
OKAY [  1.165s]
finished. total time: 1.452s
rebooting into bootloader...
OKAY [  0.020s]
finished. total time: 0.020s
archive does not contain 'boot.sig'
archive does not contain 'recovery.sig'
archive does not contain 'system.sig'
--------------------------------------------
Bootloader Version...: 4.18
Baseband Version.....: N/A
Serial Number........: XXXXXXXXXXXXXXXXXX
--------------------------------------------
checking product...
OKAY [  0.040s]
checking version-bootloader...
OKAY [  0.023s]
sending 'boot' (4944 KB)...
OKAY [  0.654s]
writing 'boot'...
OKAY [  0.172s]
sending 'recovery' (5446 KB)...
OKAY [  0.712s]
writing 'recovery'...
OKAY [  0.193s]
erasing 'system'...
OKAY [  0.055s]
sending 'system' (471804 KB)...
OKAY [ 60.282s]
writing 'system'...
OKAY [ 23.357s]
erasing 'userdata'...
OKAY [  1.023s]
formatting 'userdata' partition...
Creating filesystem with parameters:
    Size: 14442037248
    Block size: 4096
    Blocks per group: 32768
    Inodes per group: 8176
    Inode size: 256
    Journal blocks: 32768
    Label: 
    Blocks: 3525888
    Block groups: 108
    Reserved block group size: 863
Created filesystem with 11/883008 inodes and 96825/3525888 blocks
sending 'userdata' (137526 KB)...
writing 'userdata'...
OKAY [ 27.078s]
erasing 'cache'...
OKAY [  0.050s]
formatting 'cache' partition...
Creating filesystem with parameters:
    Size: 464519168
    Block size: 4096
    Blocks per group: 32768
    Inodes per group: 7088
    Inode size: 256
    Journal blocks: 1772
    Label: 
    Blocks: 113408
    Block groups: 4
    Reserved block group size: 31
Created filesystem with 11/28352 inodes and 3654/113408 blocks
sending 'cache' (9052 KB)...
writing 'cache'...
OKAY [  1.751s]
rebooting...

finished. total time: 115.545s