There are some complex ideas at play in this simple fic. First of all, the Doctor/Master relationship does often seem to be couched in terms of zero sum, where one's loss is the other's gain. I like the idea that this is in some way equality -- it's a distorted lens for the issue that fits the Doctor well.
The Master's choice to die was an ultimate act of subversion - doing something that was his loss, but the Doctor's as well. But in a way his choice almost enforces that zero sum duality. He knew his death would be a loss for the Doctor, so it became a gain for him.