Headcanon: based on the other pictures of a destroyed town and pictures of Trixie everywhere, I'm guessing Trixie somehow harnessed the power of king sombra's dark magic and will wreck havoc on ponyville. Here's hoping
That would make up for Sombra's utter lack of things to say. His villain power lies in his overwhelming presence after all. So if Sombra could somehow be relevant even after death, that'd be a massive plus for him.