I'm going to have to say that I disagree because we are asking for a mod that can AT LEAST put the characters back into the world in certain locations, and still have the same diaglogue options as the ones in the chapter before the ending (the same state of time as stated in the prompter after the credits, when you are spawned in Kaer Morhen), thus not asking for voice actors. And just because another largely anticipated open-world RPG game comes out, it does not mean the modding community will abandon the Witcher especially when the game is still young. I don't know what you mean by a "good" modtool but it certainly is a bit restricted but surely in time it will improve as CDPR stated. I believe that the Witcher 3 will definitely not be the last we see of that world, but as the developers stated it most likely be the last of Geralt as protagonist. And they have stated that they would provide the same support if not more for the 3rd Witcher installment, so they will certainly be still patching the Witcher 3 up whether or not it will relate to our issue here. But yes, I have the same game plan as you . Read, read then replay replay.About the mods. Well I don't think that we will get some kind of a mod which puts main quest characters into the world. It would be hard plus the voice actors would be hard to get like you said and Fallout 4 came out today so almost every moder will forget Witcher 3. I don't even know if CDPR made a good mod creating toolkit for witcher.
Anyway maybe CDPR will continue the story of Geralt themselves without books or anything because these games were a big success all around the world. Shame CDPR doesen't want to change anything in this game except 2 DLC's to add to it