In order to protect their son from the events that would transpire during "The Great Purge" of 2015, Foster's parents deliberately sent him to Stanford University, an American college located in Silicon Valley, California. As resistance fighters in the movement to rebel against the Observers regime, they were privy to knowledge of the Observers plans. Later, during "The Great Purge of 2015," Foster's parents were dragged outside their home and killed "like dogs in the street."
While relaying his parents' story and personal history to Henrietta Bishop, Foster said he "knew right away why his parents sent him away." While at Stanford, with a girl in his bed, a friend told him to watch the news. He returned to the common room and watched the televised footage of "The Great Purge." Watching what the Observers did to people that day was the main motivating factor involved in his decision to join "The Resistance ." Foster was an integral part of the efforts to locate and free Walter Bishop and the Fringe team from Amber. Foster also engineered a way to repair Walter's damaged neural pathways by utilizing pieces of Walter's brain that were removed by William Bell and stored in the city at the old Massive Dynamic building.
At first a sceptic, he was convinced that the Fringe team was still alive when Etta brought the ambered Walter Bishop to him. He and Etta tried to remove the other Fringe team members out the amber to get their help destroying the Observers. According to legend, the Fringe team had found a way to permanently expel the Observers from the world. Walter, Etta, and Simon returned to the location of the other Fringe members, but the device that would knock Peter out of the amber before it solidified broke. Simon sacrificed himself by pushing Peter out of the way before the amber hardened. By the time Fringe Division, at this point a puppet of the Observer overlords arrived at the scene, the Resistance members had fled the area, leaving Simon trapped in amber.
The Observers recovered Simon from the amber and began experimenting on him in their Harvard labs. Henrietta and Peter discovered his decapitated head hooked up to a machine, blinking and possibly still alive. His final fate is unknown.
In the Final Timeline, Simon would probably still be alive due to the Observer-less world.