We all know that Data would always mourn in his own way. Mourn the death of his father, mourn the death of his daughter, his mother, his brother.
So I would like to think that when he overcomes his emotional stunt (without the chip), and becomes emotionally stronger (or whatever) that the full force of realization that he's the only one left of his family just full stop hits him all at once and Data just cries. Just full on gross sobbing something fierce. Before the coming days though he would act off before he has a breakdown. Data would tell himself he's fine but feel this deep feeling of sadness and wisfulness. Deanna would feel this and the crew of the enterprise would not let him mourn alone. They would remind him that they are his second family and will always be there for him, and to just work out his feelings.
When Data finally defeats his brother one last time I would like to think that he gingerly placed a kiss on Lores' forehead before he actually died.
I would like to think they had a discussion one time that if one of them dies or that Lore dies before Data, to just cremate his remains, and to just spread them on each planet and a piece of space that the Crew travel to.
I also would like to think that both Julianna and Noonian watch over their sons in spirit. And once Data truly passes on, Lore, Soong and Julianna would be waiting at the crossroads to greet him.
