I think the days of the unknown and waiting for the inevitable are utterly grueling. It's an insecurity that's hard to describe unless having experienced it.
So sad reading that you're all going through this.
Sounds like your dad has found peace through this. And I think it's a natural response to lose focus on your creative energies. Not that it can't come and go through all of it. Chunk up the writing goals if you can for the time being. It's hard seeing the forest through the trees. Finishing those 200 pages honors him. Grief is a process.
Sending virtual hugs your way.