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