Does anyone know approximately how long the last stage of Acute Myeloid Leukemia lasts from going out of remission to death? My dad is 80.

My dad got diagnosed with AML on September 2, 2019. He received intense chemo then went into remission for 8 months (he also had chemo 5 days on 21 days off, with oral chemo every other day). He really fought hard and still thinks he's going to beat it. How long will it approximately be from here to death?