Dis never meant for this to happen. This was not how it was supposed to end for them, any of them.
When she hugged her sons good-bye, she had tears in her eyes. Her little dwarflings were all grown up. When her eldest leaned in for the hug, he told her not to worry. He told her everything would be ok, that they would come back to her. When she hugged her youngest son, she made him promise. She had given Fili his father's hair beads the night before as an honorary coming of age gift, so she gave her youngest son a rune stone. He was reckless, she knew, but he was loyal to a fault. But that is just what it might become, a fault. She made him swear that he would return to her. Her promised on his father's grave that he would, and he kept his word.
Dis had fallen ill while her sons were away with their uncle. She knew she would not have survived as long as she did had she stopped fighting. Oh, how she had wanted to give into the darkness that surrounded her, to finally be at peace with her husband and late brother. But her sons had promised to return to her. Not to the Blue Mountains but to her, so wherever she was, that was where they would go to. When she breathed her last, she had tears streaming down, for she knew she would see her sons soon.
She saw them fighting on the sides of Erebor from where she sat in Mandos. She saw their loyalty to each other and to their uncle. She saw her youngest go down first, with an ax in the back. She watched as the elder crawled over to him, already wounded, but staying strong for Kili. She observed them as Kili cried in pain, that he wouldn't be able to keep his promise to her. But he was fulfilling the promise he made the day he left Ered Luin. She looked on with tears in her eyes as he gripped his rune stone. She watched the life slip out of both of their eyes as they lay in each other's arms.
Dis welcomed them when they entered the Halls of Mandos, crying, for she regretted ever making them promise. They shushed her and said they were together, that was all that mattered, Erebor or not. So there they stood, the line of Durin gathered together, Thror, Thrain, Thorin, Frerin, Dis, and her two sons, Fili and Kili.
She still believed that this was not the fate that her sons should have endured.
AN/ I am not sure if all of the facts are accurate, but I did my best to try and stay cannon. I am not sure when Dis past away, as it is unspecified on all the websites I checked out. Your feed back is greatly appreciated! :)