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If gnome-shell has locked, try the following

Switch to a different session by hitting:
Ctrl+Alt+F5

Now, log in.

Find the gnome-shell process id:
ps aux | grep gnome

Look for the process id for this process:
/usr/bin/gnome-shell

Restart gnome-shell with the id you found above:
kill -HUP 1111

Back to your session:
Ctrl+Alt+F7

Everything should be largely intact.

Note:
If you get the process id for the gnome-session, rather that the gnome-shell, you'll be logged out and all your processes associated will be terminated.