Isn't the plan the same thing as the knot? Where are the layers intertwine.What is Knot? Where it is? Is it Plan area or Temple?
EDIT:
Oh my gosh, this is so usefulMurtaugh went to the Knot where all seven Layers converge and saw the kind of chaos and destruction that he unintentionally wrought all these years ago from the Lighthouse and the Core. He never saw anything like that over all of these years because he's always in all seven Layers at the same time. It was when he arrived at the Knot that he fully understood what has happened and fell to his knees in disbelief and grief. Liz then approached him to talk things over, protecting Mur from being killed by victims of the Collapse.
Murtaugh then spent his final years fixing and repairing all seven Layers from collapsing any further, though he was unable to restore the Third Layer, his home Layer, to its former glory. All he could do was to stabilize the whole Layer. That's why the Karma Portals we used in Sub_7 didn't caused the entire dimension to collapse because Murtaugh already stabilize the whole Layer to keep it from deteriorating. Mur soon died of old age, regretting deeply about what he has done, the kind of chaos and death that he accidentally wrought until he experienced a vision from Shiva about the future of Submachine. He soon died in peace, indicating that the Submachine Network may survive and possibly thrive once again sometime in the future. The people and Liz soon buried him underneath the Temple in his honor.
Then Liz took up the mantle of Murtaugh to resume his work, making sure that the Submachine Network remain as it is before her death. The people soon buried her next to Murtaugh under the Temple.
Years has passed and the Submachine remains as it is, stabilized yet not quite as whole as it was in its former glory.