> Sure, but is a low quality life worse than oblivion?

Unequivocally yes. I think you are drastically underestimating how bad a life can get.

> Plus, if the suffering experienced by this patient helps cause someone else (or many someones else for centuries to come) to have a higher quality of life, one person's suffering can buy a lot of QALYs.

Exactly, that's why I'm arguing that this person's choice is brave.