Spike is no longer the goblin boss at the windmill, they changed that. Probably because too many killed him accidentally without Wyll in the party and thus aren't able to advance his story.
Spike is now always in the Shattered Sanctum, torturing that adventurer and you get the scene there.
I'm not sure Spike was ever the goblin boss there. The boss' name is Fessek, or something close to that.
Fessek is the one who held Wyll down while Spike took his eye.
That scene had a strange bug in Patch 3. After Wyll questioned the goblin boss, he said (perhaps telepathically), "Kill him." If you actually followed through on that and killed him, Wyll would get upset, as if he didn't get to interrogate the goblin first, or as if he didn't just ask you to kill the goblin.
Before Patch 4, there was an opening dialogue to that scene, if you walked into it without attacking first. That's when Wyll makes a point about not killing Fessek, and all the Spike stuff comes out about his eye.
Unfortunately, that scene isn't playing anymore. At least, I can't get it to trigger.
The end scene is playing, though. Wyll gets his chance to interrogate Fessek. Sometimes. I had to fight that scene out three times before I got the ending to trigger. The first two times it didn't trigger. Fessek surrendered, but Wyll never jumped in with his "Let me question him!" dialogue. Instead, Fessek pleads for his life and offers information about how to sneak into the goblin camp.