What is the life expectancy of someone with Superficial siderosis?

I really cannot fathom that I’d there are only less than 300 known cases that researchers would spend much time researching this debilitating disease. As for life expectancy.....my big burly, active husband bumped his head 16 months ago, had a brain bleed, superficial SIDEROSIS.......and had been through pure hell since. He has lost over 50 pounds, often lays in the fetal position for days not eating or drinking. He can hardly function. He is off balance, weak, major hearing loss, eyes get crossed sometimes, confusion is often, denial of his condition, time has no meaning, and so many
Other symptoms. The most debilitating symptom of all is extreme and continuous headache, always a 3/10 or higher making it very difficult to concentrate on any task. I feel his life expectancy is not too far in the future. He may be healthy, but the pain and the drugs he must take are rendering him Inactive, with him being horizontal in bed most days.
His muscles mass is gone, he can hardly walk any more. I fear for him.