Dude, Disney just closed Miramax a couple days ago... not the best case scenario. Even worse, Nintendo buying Sega could turn into a situation like Vince McMahon's WCW. He got all this talent and all these assets then had no idea what to do with it.
The problem with buying Sega and gutting them is that many of their major designers from Sega's golden age are long gone, namely Yuji Naka, Yu Suzuki, and Naota Oshima. Ultimately, they do get the IPs and while Nintendo could exploit crossovers for games like Mario Party, Mario Kart, Smash etc., I wonder if they would even know what to do with say, Shining Force, especially when they have Fire Emblem.