Language is a living evolving thing. Locals can still speak Cantonese without it being diluted by Putonghua. Up to the locals to keep it alive. Pushing Putonghua in a chinese city is par for the course.
I speak Hookien as a chuld and learned it from family and I still speak it today when I visit the home town. Meanwhile I use Putonghua for business. Only those who have an issue wirh China make a big stink about it.
Point is Cantonese can be preserve even if not used in schools. I guess monolingual speaking folks will never get it