Concept - The Doctor goes to deserved rest.
Far future. One of next The Doctor’s incarnations goes to fix another conflict. Doing this he will lost lots of important things - companions or another close people. Finally, The Doctor finish his mission. He tired. He take decision to go to rest. He goes and throws down his screwdriver(it smashes). After that, he take the look on his dead TARDIS and after all, regenerate into new and last incarnation(maybe it wil be The Curator).
viddharta-joshua