An unclean shutdown can damage the Xfce panel. Fortunately, this is easy to fix.
Log out of Xfce. Log in again, but into another desktop environment or window manager. Now recover the panel from your most recent backup, which you will find at ~/.config/xfce4/panel.
What? You don’t have another desktop environment or window manager? Or you don’t have backups? Then you can create a new user, log him in to Xfce to create a default panel, and copy it to your panel’s location. Naturally you’ll need to log back in as yourself and tweak your panel as desired. Then you can delete the new user’s account and files.
And let this be a lesson to you: always have a second window manager installed, and always perform regular backups.