Thank you for reading it, I wasn't sure someone would.
For the beginning of the story on how he does not accept inevitability, I was thinking of showing how this character is stuck in this old messy house, basically in a state of "not living" like an hikikomori; like this I would create a situation where not accepting inevitability means to stop living in a sense.
As for the stages of grief, I would use them only as a environment inspiration just to give some sort of theme for the various locations; I'm not really a fan of "spelling things out" to the player so probably I would keep the stage of grief for myself to evade the risk of being preachy.
I'm glad you liked the idea, I too think it would interesting to develop, especially the locations and gameplay