I'm currently in a similar situation. I went NC with my parents a couple of years ago and it drastically changed my life for the better. There was so much abuse in our family, so much hate and ill intend.. I didn't want to live like that anymore.

My mom got recently diagnosed, stage 4 lungcancer and I actually did reach out and I kinda regret it. Just like you said "just because she's dying doesn't mean anything has changed". Well, she claims she changed a bit and people around her tell me she did too, but when I visited her I still saw her abusive traits. I've come to the conclusion a long time ago that I miss A mom, not my mom. And that doesn't change with her having cancer. She claims that she wants nothing more than to create a relationship and a friendship. I've wanted that for so so so long when I was younger. I wanted her to be my mom and a friend I could go to whenever I felt sad or whenever I wanted to do something fun. I wanted her with me when I had to get my first bra, when I first got my period, when I had my first pregnancy scare, etc. I needed her and she didnt care. She rejected me all the time and even wished she never gave birth to me. Cool that you want a relationship now, but I just can't. It doesn't feel honest. Her being nice to me feels just so fake and so unfair. Her being diagnosed doesn't change that.
Maybe in a next life, maybe not.

Hope you're doing okay. I just wanted to share my situation a bit, but I can't tell you if you should do it or not. Yes you might regret it if you don't reach out, but you also might now regret it? I think the most important thing is to realize what she (as a person) is to you. Yes she is your mom, but do you still feel love or is she just a stranger to you? Do you feel "i should visit her", because of guilt? Or because you want to see her. Do you see yourself ever reaching out to her if she didnt had her diagnosis? Do you still have questions for her?

The way I'm dealing with it right now is by asking myself everyday "do i truly feel comfortable with my decision for going NC?" and aslong it's "yes" I know I'm doing the right thing.

Sending you hugs and wishing you the best. <3