the way it was with my parents was that they needed to fill the physical hole, not the emotional one (as I agreed it would have been wrong to try to replace Wills). their house was like a mausoleum, the place screamed of aching emptiness. I felt they needed another dog to fill that, to allow them to grieve emotionally, alongside the new dog.
It did work, much much better than I had hoped. The day we got chuffley made me understand the meaning of bittersweet... proper smiles at the same time as the tears. weird feeling.
Edited to add: the discussions that led up to us getting Chuffley were harsh. My mum felt I didn't understand, I was being cold, insensitive, unfeeling. At any other time I would have backed off... but I kept on... and it was a really really hard thing to do. the day they got chuffley my mum gave me a hug and said "thank you, you were right, I didn't see it then. Sorry for the things I said, you were right, thank you for persevering"