GOSH!!! Sorry to hear that.
Only the wide panel broken? still functioning?
If still working, then its not relly a bad day, unless you uses the wide panel often.
The warranty is over. It is a spare flash, think probably bring it to the Service Center when free or sell it at B&S.. It is still working but without the wide-angle panel and catchlight panel function only.
I suggest you bring it to the service centre and see if they will fix it for a small fee or for free.
If not, I think this part is a low stress area, so superglue would be suitable to reattach it...no harm trying. Just don't get glue all over the rest of the unit and be warned some glue vapours become opaque when it comes into contact with something (eg Shelley's super glue) so don't let it near your flash's front lens cover.
good luck