huge sympathy to everyone on here, especially you OP 
I lost my mum over 27 years ago, at the age of 23, to breast cancer. She was in her early 50s.
Like you OP I didn't have the best relationship with mum when I was younger, I was an angry teenager and didn't cope well with adolescence, she found it hard to understand me. Our relationship was very much improved by the time she died and I was enjoying connecting with her.
It has been hard since I'm not going to lie. All of the things you and others have mentioned have been tough, not having her around for significant moments, her never meeting or even knowing about my kids etc etc etc. I went on to develop alcoholism and deep abandonment issues. Whether they were directly related or not who knows (I had always struggled a bit). I still miss her.
But, I'm also strong and resilient. As PP said I know first hand how fleeting life is and how close any of us really are to death. I know that the worst CAN happen. I know that life is short and we need to make the most out of it. I've left bad relationships on the back of knowing this, I've overcome my alcoholism and other MH issues on the back of it, I've invested in myself and my own happiness on the back of it.
I have two DC and I talk often to them of my mum. They know how much she would have loved them. I don't go on about it but sometimes when they do something really funny I tell them she'd love it, or I relate some funny story about her. They are teenagers now so when they play up I often remember how fraught my relationship with her was when I was their age and I feel optimistic we will get through it. I look forward to being in their lives when they are adults (although I'm never quite convinced I will be I try to stay optimistic!)
I feel life is precious, my kids are precious and I try to make the most of every moment I have with them.
I know I do have a constant sense of loss still though, and even in the happiest moments I am very aware they will end. It's like life has a tinge of melancholy, even in the most joyful moments. But that's ok, it's real and I appreciate that.
I wish you the very best OP. It is very tough but time does heal the worst of the pain and acceptance comes when it is ready.