Well, the most important thing would be the elimination of one third of the mainstream gaming consoles. If either company went under (which will never happen, of course), the other company would see an enormous increase in sales, due to reduced competition.
As for the studios, it would be similar to what's happened with THQ. First, they try to sell off the studios, and people like Turn 10 and Naughty Dog would be snapped up immediately for large prices. After that, they sell off IPs like Hot Shots Golf to the highest bidder. None of the big franchises or studios would disappear.
It's harder to tell with Nintendo because it feels more like one big development house. I guess they would just need to name the different teams.
(Former) Lead Moderator and (Eternal) VGC Detective 
