Recover a deleted directory

[Moltke]

Hi everyone! Hope you're all having a nice life!

I need some help here please, I accidentally deleted x86_64-linux-gnu directory from /usr/lib/x86_64-linux-gnu and now nothing works; no thunar, no browsers...I'm writing from a live session and tried to recover the directory with extundelete by following instructions from here: http://extundelete.sourceforge.net/ but when trying 

Code:

sudo mount -o remount,ro /dev/sdb5

I get the error

Code:

mount: /dev/sdb5 not mounted or bad option

       In some cases useful info is found in syslog - try
       dmesg | tail or so.

  So, as instructions explained I simply unmounted the partition and ran

Code:

sudo extundelete /dev/sdb5 --restore-directory /usr/lib/x86_64-linux-gnu

but I got

Code:

extundelete: Bad magic number in super-block when trying to open filesystem /dev/sdb5

I also tried with gparted  >device> attemp to rescue data option but it didn't work. I have performed all of this actions from the live session, haven't written anything on the disk since folder was deleted cause I know there are more chances of recovering the data that way. Can I recover that folder? or will I have to reinstall LL?
Any help/advice is really appreciated. Thanks!