How to deal with a parent feeling “ready to go” as in passing away?

Context I’m 22, my dad is 41, and mom is 40
I don’t use drugs, never have and am completely sober

TW drug addict parents

My mom isn’t in my life anymore after the age of 18/19 since she has been a drug user/ alcoholic my entire life and has been abusive.

My dad is a different story he smoked cigarettes on again off again throughout my childhood and drank occasionally. He never did drugs other than weed when he was young but never did it around me. He also was sober from everything for 3-4 years during middle school. My mom and his relationship though was super toxic and pushed him to his limits. He helped me a lot with my mom’s abuse. He truly was my best friend and biggest supporter through all of that. When I was about 19 he was talking with me and he told me he had to be honest with me about something and told me he was smoking meth. I figured it was because of my mom and she got him to try it and I also knew he told me because he knew how messed up I got over moms drug addiction and how many times I tried to help her. Some context my dad who I call dad is my stepdad my mom got with him when I was 8 and that’s when I met him. She never let him adopt me legally and held that over his head the whole relationship and used it as a way for him not to leave her or she’d take me away from him and so he stayed.
I haven’t been able to talk with my dad regarding his drug use these past years (ages 19-22) but I reached out to him last week and asked if he was still using and explained the guilt I felt -even though I know it’s not my fault- how I cared about him and hope he is doing okay.

He first off told me never to feel any guilt, I knew he would say that and that he made his choice and he’s glad he put me first during my childhood and wished he could do more.

He is still using off and on I guess and I don’t really know what to do with that, I asked if he wanted to go to rehab and he said no so I don’t know how to help him you know?
He also told me he’s just kinda “ready” to go and I don’t know how to handle that to be honest. What do you do when the only parent who was stable during your childhood and like your best friend just tells you they’re ready to die? I used to have nightmares about him dying as a kid, so I think it also just triggered those old emotions. I’m still trying to sort out what to do and I know he didn’t tell me that to hurt me -he sent it in a voice message and I could tell and hear how he was just being honest- frankly that sucks hearing how tried he is with life, I don’t think I’m ready to loose my dad yet. It makes me feel selfish and like I’m a child who’s not ready to let go. I know how it feels to be suicidal and I don’t ever want to make him feel bad for feeling this way. I tried to support him the way I could by telling him I’m here and I’m sorry and trying to give him any sort of support and let him know I’m here to help and a big speech about how I’m here and it’s okay. I just am at a loss to be honest if my dad dies soon i genuinely don’t know what I’m gonna do. I’m only 22 and I’ve already lost my mom, she also treated me pretty badly. It’s complicated too since he’s not even that old he’s 41 but he has some health issues with a tumor he has on his face.
For context it’s a tumor in his lip the doctors said to remove it since it’s connected to a main blood vessel in his face he might die from the surgery and it’s also very expensive.
So my dad weighed the options when I was around 15/16 and decided not to do it. So I am pretty sure that also plays a big role into why he’s ready to go/ why he also might’ve started to use drugs?

I wanted to know if anyone related to this, had any advice or had questions?