Yeah i guess cos its bonded you could look to replace both rear stays, but £££s.
Kinda looks like the bonds at the stays have been gunked back together already? And having looked again both are bent, as well as the crack. Looks like its taken a proper impact at the back?
Oh it's snapped even? I thought there was just superficial damage.
Then it may be beyond economic repair. I suppose you could swap a tube as lugs were used... but it becomes £££ then.