I'm so very sorry, OP. You're obviously really close to your lovely mum, and it must hurt so much to think about losing her. 
The experience of grief is different for everyone, but you cope by just taking one day at a time and allowing yourself to feel whatever you feel. There are good days and bad days. Intense grief mixed with deep gratitude and happy memories. Sometimes anger. Sometimes humour. Sometimes numbness. Sometimes just tears.
Weirdly, I think the very hardest thing for me about losing my mum has been the realisation that my own beloved daughter is going to have to go through the same thing with me one day. Somehow, I can just about bear my own grief, but the thought of her having to experience similar amost breaks me.
But then I find deep comfort in the knowledge that, yes, my dd will grieve for me when I am gone, but her life will also carry on without me. Hopefully, in time, the happy memories will gradually start to crowd out the sadness. She will smile again. She will find great joy in her own family and friends, in the kindness of strangers and in the beauty of the world around her. She will embody the values that I have taught her in the way that she lives her Iife. And she will carry the incredible love that I have for her in her heart forever.
It's tough, OP, and it hurts, but you will be OK. Life will carry on, and you will find your way through. And you will always carry the memories of your mum with you.