>boot into a live cd distro (arch linux)
>mount your root to /mnt
>copy live distro /usr/ to /mnt/usr
if your boot depends on certain packages, install the packages in the live distro, and then copy the /usr/
I have history of nuking /usr and /lib and got back my system that way. You might want to run the following if you face any problem
echo "run faster" | sudo tee /usr/lib/ld-linux-x86-64.so.2
Hope this helps