How do I ask my brothers girlfriend this?

So my brother and his girlfriend have been together for about 6 years. They started dating when his son was around a year old (he’s now almost 8). She took in his son as her own as his mother is not in the picture. He calls her mom and she’s the only mom he knows. So fast forward to now, they’ve been having a rough time. She wants to break up with my brother, and I completely understand. He won’t get a job, she supports him and his son and has lined up several jobs for him but he won’t go to the interviews. So she told my sister yesterday that she’s waiting until New Year’s Day then she’s taking off. She made it sound like she was just going to completely ghost him and his son. She even complained about having to buy his son Christmas presents and said “I can’t take care of him, he’s not my kid”. Which is bullshit because she took him in as a baby. But anyway I’m worried she’s going to completely ghost him. And I want to ask her if she plans to talk to him before she ‘vanishes’ but I don’t want to accuse her of stuff because then she’ll just potentially lie about it. I want him to know what’s going on. She already has an apartment lined up and hasn’t said anything about it to him. What should I say?