Ouch! It was not that bad, but the system could not complete boot as one of USB drives (ext2) for some reason had a bad superblock, so boot was aborted and dropped in shell. When I get to the office and logged in as root it moved into the filesystem recovery mode. All vital systems checked clean by fsck, except this USB drive with ext2. I had to
mount -o remount,rw /
to restore read/write access and then I could replace the offending fstab with its backup copy. The box booted normally.
Then I fixed the offending disk (unmounted) with
and also replaced the ext2 with ext3 and replaced its UUID, just in case
tune2fs -j -U time /dev/sdc1
Then I updated the corresponding line in /etc/fstab and rebooted - all worked fine.