It wasn't so much that Johns didn't care what happened to Dick as he cared quite a bit. There was a lot of talk and rumor around that time, Didio's edict for FE was to kill Dick. John's again inteceeded on The character's behalf and won that battle.I don't think Johns cared. After he exposed Dick's identity to the world in Forever Evil Johns showed no interest in what DC did with Dick's character. He didn't care and the burden of what to do with Dick fell on the Batman editorial after Johns tossed his mess into their lap. At that time I don't think Snyder and the Bat editors wanted to deal with fallout of Dick's identity being exposed to the world. So the original plan was to have Dick wear a blonde wig (you see that in the Batman Eternal Thanksgiving promo), pretend to be dead, and run around in this different Nightwing costume with Tynion writing the Nightwing book as we see in the new images. The original Bleedingcool leak was that Tynion was going to write the Nightwing series, and they even had that funeral issue completely drawn before scrapping the concept for the Grayson pitch, so the Batman editors switched plans really late into the process. They had that messy Nightwing #30 by King and Seely to try and act as a bridge to the Grayson series that had 3 different stories in it.
I still think the main reason for going with the Grayson idea was because Snyder and the Bat editors didn't want to deal with the fallout of Dick's identity being exposed to the world. Realistically this event should have had BIG impact on the Batman mythos, especially if Dick was still in Gotham as Nightwing, but dealing with it properly conflicted with what Snyder and the Bat editors wanted to do with the ongoing Batman story. They didn't want to change plans and include this major plot all of a sudden. So their solution was to remove Dick from the Nightwing identity and move him across the ocean where they could ignore the exposed identity thing. Which worked as the identity thing really had zero effect on anything and "Dick's death" became the bigger issue to overwrite the exposed identity problem. To this day it made no sense for Dick to lie to and pretend to be dead to the Batman family because in the end Dick's identity being exposed lead to nothing. No fallout with intense media pressure and no villains using the information to get to the Batman family. Nothing happened. Which tells me that no one in the Batman office wanted to deal with it.
Also speaking of Tynion in some interview before all this he talked about how he didn't think Dick worked as a solo character. So I remember me and others being upset he was the one rumored to be writing Nightwing's solo after Forever Evil when he said he didn't think the character worked as a solo character. But in the end we dodged a big bullet with that series and got the Grayson one instead.