Sign up with GoogleSAA don't own the Boeings anyway, they lease them and then lease them to Mango at about 20% of the lease price, can't remember the exact figures now. They sold all their planes a couple of years ago and then started leasing so they could magically be catapulted back into the black from being billions in the red.
Apparently one of the major reasons for launching Mango is to get out of major union contracts that SAA's locked into. Ultimately most of the local capacity will be transferred to Mango with SAA focusing on long-haul and regional. As its a separate company they'll be able to renegotiate all the employment contracts etc. No surprise that just after Mango launched SAA are retrenching 1000 staff!