OP please seek some bereavement counselling, I think (as anohter said) you are mourning your mum, maybe not as she was, but as you would have liked her to be. Maybe circumstances in life meant she could not be that mum, but maybe in her death you can now find a peace.
Whatthefucknameisntalreadytake "I won't be informing him if she is unwell or dies. I wouldn't give him the option of coming to her funeral when he isn't there for her in her life. I appreciate people stop contact for good reasons but I don't think you can then expect to be kept in the loop with important events." I am not sure you can consider the knowledge of whether a parent has died or not being 'in the loop'.
No matter how much you dislike or disprove of you brother's choices, please do not deny him the knowledge of whether your mum is very ill or dies.
I've lost both my parents now and you don't get a second chance to go back and do it differently. So please, please be as supportive as you can be to all, put your own feelings to one side.
If your mum wants you to make contact with your brother do it for her, if he comes, it is for your mum, not you, if he comes for the funeral, it is for your mum, not you. And at the very least please tell him if she does. Please do all you can that you will not later regret something. This is as much for your as for your mum or your brother.
Music "There was a thread on here recently where the mother expressed that she did not want the NC daughter to be informed of her death. Perhaps you mother made the same proviso?"
I did wonder that too. But even so I think the aunt and cousin would be wrong. Life is for the living and the dead do not get to constrain us with their requests, only to decide who to give their money to IMHO.
scottishdiem "I am not sure why you think that your aunt and cousin should reach out to you when they may not be fully aware of all the circumstances of being NC and also maybe only hearing your DMs side of things so may not have been inclined to speak to you either."
Because it is the decent and human thing to do, and to not do it seems to me a very cruel, and unnecessarily cruel, thing to do.
"I am not sure that their death supersedes the NC." Yes, to me death does supersede NC. This is knowledge and information not contact.
"I am NC with a sibling and will probably miss a lot of information (suspect they got married recently for example but no-one speaks to me about them and thats they way things are and its what I wanted)."
But a relative getting married or having a baby is very different from them dying. Especially because in most cases of N/C there is a lot of pain involved. Why allow a relative to go on living with the pain when in some ways knowing of the death may enable some degree of healing and coming to terms?
Maybe now the OP can grieve for the mum she wished she had, I think finding a place to visit would be good, maybe planting a tree, not so much for your mum, but for what might have been.
Thinking of you OP.