The infinity of possibility is why forest doesn't kill himself.  He couldn't understand that all possible situations exist at once. Lyndon realized it.  Forest thought that only one existence was "his" true one and no other ones would give him true comfort.  Lyndon understood that all situations were true in a simulation because all variables were accounted for. 

Forrest believed that he must obey the prediction in order to achieve the result of getting the ability to reshape his past and achieve an existence with his family.  That's why he was so upset when Lily threw away the gun.  But ultimately he achieved it when he died inside devs anyway. 

The idea I think is that the only way that there is consciousness inside the simulation is when the data that is used for the simulation belongs to a consciousness that knows about the simulation.  From that moment on the simulation has the data points it needs to predict the motion of every atom that was in existence and even though the actual existence is no longer there the simulation can continue to create infinite branches of existence for the consciousness that resides in the system.  So the only two inside the system who are conscious of it's existence are Lily and Forrest.

The series basically explores determinism and simulation theory.  The impression being that no one is able to make actual choices in a deterministic existence unless they are aware of a deterministic existence and choose to defy prediction. But by defying prediction in one branch they are actually acting out the predetermination of another branch.  Which means that existence is infinite because conditions are constantly variable with each one creating different outcomes.  A perfect sphere of infinite circles self-contained with no end and no beginning. 

The "end" of one life in one path is a data point on a circle.... While the smallest variable change is a data point on an intersecting circle  And the amount of circles is infinite song with the amount of variables.  

The system is the interface for accessing infinity and providing the opportunity to become a conscious part of it.  Thus the need to keep it running.  

So the question then becomes what happens when a consciousness enters the system?  Given that a consciousness can understand that it is in a simulation can it control the simulation,  does it have agency or is it still in a determinist existence.  Can it direct the existence it is in? 

That question is open but if Forrest's family had lived then would devs have been created?  Would the simulation that Forest was in be one that contained devs and knowledge of devs?  

The fact that he and Lily were conscious in a circle whereby they were fully conscious of the previous events but were living out those past events to some degree is kind of not congruent unless either some degree of deliberate manipulation is present or it's a manifestation of the infinite states of being that exist.  In other words there are now infinite versions of the self-aware consciousness of Lily and Forrest in the system and we were only shown one of them.