Is it possible to get NPCs to interact with part click detectors?

No, not directly. It is possible to emulate the ClickDetector being clicked using BindableEvents. I would just add a listener for the bindable event in the script with the click detector. Then when the NPC "decides" to help the player, it could fire the event with the player argument as NPC or something. Example code below.

Part Script:

function PartClicked(plr)
    if plr == "NPC" then -- Optional if you want to change what happens when a bot clicks it
        --Do stuff
    else --Real player clicked it
        --Do stuff
    end
end

event.OnEvent:Connect(PartClicked)
clickDetector.MouseClick:Connect(PartClicked)

NPC Script:

function HelpPlayer()
    event:Fire("NPC")
end

I hope my answer helped you, if it solved your problem, please remember to mark it as correct!