I can confirm that not pulling the switch will leave Agrippa's neck enjoying a pleasant breeze, as i decided not to save him on my second playthrough. Further confirmation from the scripts below:
From the first nave map:
void ChangeChannelingLever(string &in asEntityName, int alState)
{
    if(alState != 1) return;
    
    AddDebugMessage("Turned channeling on chaneling machine!", false);
    
    //Stop any strained talking going on
    StopAgrippaStrainedSpeak();
    
    //Lever is now stuck and will not move.
    SetLeverStuckState("channeling_machine_lever_1", alState, true);
    
    SetLocalVarInt("AgrippaVoiceMachineOn",1);
    
    SetGlobalVarInt("AgrippaActivatedIn21", 1);    //Agrippa is awake in 26 too
    
    AddTimer("AgrippaNormalTalkStart", 2, "TimerAgrippaNormalTalkStart");
    
    //Add effects on machine
    CreateParticleSystemAtEntity("ChannelingMachinePS", "ps_channeling_machine_smoke", "AreaChannelingMachine", true);
    
    PlaySoundAtEntity("ChannelingMachineStart","21_cm_reverse_low.snt", "AreaChannelingMachine", 0.05, false);
    PlaySoundAtEntity("ChannelingMachineRunning","21_channeling_machine.snt", "AreaChannelingMachine", 2.0, true);
}
Notice the SetGlobalVarInt line. This global variable determines if agrippa has a head in the second nave visit:
void InitAgrippa()
{
    // Check if player has awakend agrippa in 21, if not make Agrippa dead.
    if(GetGlobalVarInt("AgrippaActivatedIn21") != 1)
    {
        SetEntityActive("agrippa_2", false);
        SetEntityActive("agrippa_headless_1", true);
        SetEntityActive("AreaAgrippa", false); //Turn off no item use on corpse is possible.
        
        StopSound("Sound_60", 0.0f); //Channeling machine
        DestroyParticleSystem("ParticleSystem_62"); //Channeling machine
        
        SetLocalVarInt("AgrippaDead",1);
        
        SetEntityActive("bone_saw_1", false);
        
        InitWaterLurker();
    } 
    else
        InitMissingIngredients();
}
So, going to have to load a save from just before you were captured and save him if you want the Agrippa ending.