Family heartbreak. Any suggestions for handling the situation?

Perhaps it's best that you just let it be, as if your mother doesn't know who he is,(because it's been so long since she's seen him and because if her dementia)it won't really matter if he visits her or not anyway, as she won't remember that he was there or not. Just like she probably doesn't remember when you come to visit either, even though she may still know who you are.
Or if he changes his mind and decides he wants to visit again, tell him to just introduce himself with his name and that he's her son when he walks into her room. That might be helpful for them both.

I was estranged from my mother for over 20 years, and when she was on her death bed, I walked into the room where she lay, and she asked me who I was. I just responded with my first name, and she just said "oh." It didn't bother me that she didn't recognize me, as it had been a long time since she'd seen me.
And even though I had made peace with my extremely dysfunctional childhood, and my parents many years earlier, for my mental health, I chose to distance myself from both my parents.

So give your brother his space and let him decide what is best for himself.

My dad passed away with ALZ 12 years ago. I’m now taking care of mom with ALZ. Towards the end, I believe my dad thought I was just one of the aides at the facility even though I visited him every day. My brother said he couldn’t stand to see dad that way so only visited him briefly twice in the last 18 months of his life. He’s now the same with my mom. I see mom every day, twice a day and there are days now when my mom recognizes me but is not quite sure who I am, but other days knows me immediately. I gave up on the anger I felt towards my brother years ago. He has to live with the choices he makes. He has the same opportunities to see her as everyone else. As caregivers, we have to focus on the daily reality that dementia is a cruel and heartbreaking disease as we continue our heartfelt desire to travel the path alongside our loved ones. We can’t carry the burdens of other people’s choices. Just focus your energies and emotions on your mom and her happiness.

Not a thing. He stayed away 20 years and then was surprised she didn't recognize him. What was he expecting?

What did he expect? Sounds like it is all about him, not her.

Don't worry about it, you have enough stress already.

There won’t be a next time. I won’t be back. It’s too upsetting seeing her like that."

I wonder if it's occurred to him, that it's hard for you to see her like that, too? People with a sense of duty push through those feelings. (as you have)

That said, I think others here have had some good ideas, don't give up on him visiting her, after he's cooled down. (for your Mom's sake, if nothing else)

(I would have been tempted to reply - 'It's hard for me to see you, like this, I thought you cared about someone besides yourself')

Taylorb1: Quite honestly, there is nothing for YOU to DO. As your brother had gone incommunicado for two decades and then was stunned when mother did not recognize him, your mother's reaction was understandable.

You might not like what i have to say but feel it's got to be said.
First, I'm not understanding due to lack of more info on your part.
Second, Don't you think if he wanted to talk to you all, he would have done it in the last 20 years?
Third, Did you really expect her to recognize him after 20 years??
Fourth, If you didn't care enough to speak with him and he didn't speak to you, for the last 20 years, then what is your reasoning behind getting in touch with him other than to possibly make you happy for him to come see her, which he did.
Fifth, Now he's made it very clear he will not be back which sounds like it made you very unhappy. It seems to me like you stirred the pot, and now there's nothing you can do about it except leave him alone.
Sixth, If he's interested enough to call and if you're interested enough to speak to him, then hopefully your rift can be mended.
At this point, I'd leave him alone unless he's asked for updates, which you haven't mentioned either. You've already got enough on your plate... let it go.
Good luck to you!

Is there a reason why he has stayed away for 20 years? She hasn’t seen him, doesn’t know him anymore so there is no relationship to build on. Her memory of him is gone. Not surprising. Dementia patients forget quickly therefore you can expect them to forget you if they don’t see you regularly.

Perhaps brother is just feeling hurt and furious of not being recognized without understanding real reason behind it?
I imagine, it will be hard to recognize people after 20 years, add dementia probably almost impossible even to remember.
Let him be and email again in few days/ weeks.
You should not be so hard on yourself, it is not your fault.

Your brother hasn't seen his mother with dementia in 20 yrs and he is shocked that she doesn't recognize him? Even if she didn't have dementia, most folks change quite a bit in 20 yrs.

I don't think there is a thing you can do other than maybe mail your brother some books on dementia and maybe a book or two on how not to be estranged from his family.

I see my mom all the time and she doesn't know who I am. Dementia is ugly and that first shock that they no longer recognize you is pretty devastating.

There really isn't anything YOU can do. You don't mention why there was no contact for 20 yrs. Is your brother going to start calling you now that you have made the first move in calling him? If you are never going to hear from him again, I wouldn't worry about it.