Actually one or two Nikon DSLR's have moved over to Toshiba sensors and I read there may be more to come with that sensor brand. Is this the first stages one wonders of Nikon dumping Sony for future sensor supply.
For Nikon to use Toshiba sensors I would imagine there has been some joint research going on.
Classiccameras, that is normal based on my business experience. Don't think Sony always supplied Nikon with all their sensors. New competitors come in and you diversify your supply base based on qualitly and price for the particular market. Nikon will probably contiue to purchase certain sensors from Sony, in particular the more critical ones such as the 36Mp. Believe the differences in performance A7r v D800 more in the processors rather than sensor.
Sony sensor division would not alienate a large customer to suit the Sony camera division. In USA that might even be illegal. Don't know about Japanese commercial law. Have some experience of the US situation. Olympus started to purchase from Sony and Pentax remain as they claim Sony make the best sensors.