I have a friend who's mum is terminally ill, I have been curious about this whole episode in his life because i have never been able to observe someone going through this before, I have been through it with my Pop but I was too involved to take note.
I find myself struck by the question, if my friend is not at his mums bedside when the pyshical event of death occurs. Does it matter?
From the mothers point of view, it's her death.
Common understanding of death leads me to believe that she would want all her family around her. However this does depend on her own insicurities and beliefs, and whether she has been waiting for the final moment to tell her son something.
If she has already expressed everything she wants to say, then there is no realistic need for him to be there. She may want everyone there to reassure herself that she has had a good life and the fact that all her family is there shows this. She may want to look upon them for one last time and bid them all farewell.
The opposite also could be the case, where she doesn't want anyone to be there, this is not like a wedding, it's not about anyone but her and she's the only one that can go through this, it's a journey for one.
From the Sons point of view,
he would probably want to be there as he has his own insecurities about death and doesn't want mum to go through it alone, for reasons of love, guilt, fear.
What would the effect be if he wasn't there?
I don't think there would be any, you could still share grief, you could still say goodbye. In the long term, would you look back and say i wish i had been there? I don't think you would, not unless they had died in horrible circumstances, and then your would have only wanted to be there to prevent it.
Summing up my feelings on this:
mother + family = ego in control of mother