I do not know if dental implants or a RPD is in my future. How long after bone grafting do I have to make up my mind before reabsorption occurs?

Ideally 4-6 months. The rule is 4-6-8. Ideally 4-6 months, but not longer than 8. The longer you wait, the bone starts atrophy,density and height starts to decrease. Hope it helps.
About a year, Give or take. That does not mean you cannot wait longer, its just that the bone is slowly resorbing and the volume may not be present when you do decide to have implants placed.