This is probably already here on this site somewhere, but I haven’t seen it here, but if it is, please redirect. (be aware that I am a complete noob here) If their isn’t one…
!SPOILER ALERT!
Okay, so, If I remember correctly, doesn’t Guilty spark come back at the end of one of the forerunner books? I can’t remember which one, some ONI guys searching the Arks ruins find him(well, his barely functioning form anyway), and at the end of the book, they throw him out, only to find he is now in their ship. Then Spark puts them all to sleep and sets a course to where the librarian is, which we now know (at least we think we know) is requiem. So… wouldn’t this mean we will see him on requiem? If not in campaign, which we didn’t, then in spartan ops? Also, time wise, I don’t remember if the book stated when this happend, but it did happen between 2553 and 2557, which means he is either already on requiem or heading there at this time. Now, since we haven’t seen him at all, I think its a bit more likely he is still in route, but he could already be there, and he’s just hiding or something. As to what he would do… Well, he’s probably not hostile (to humans anyway) since he seems to have contracted amnesia (somehow), and determined everything that happened on the ark was done by a different version of himself. Of course, it may have nothing to do with requiem since he’s heading to where he thinks the librarian is, but its a possibility. Although how he would affect anything thats going on is up to 343, although palmer would probably just shoot him.
Again, I apologize if this is already on this site somewhere, and please redirect if it is. But I haven’t seen it, so… just though I would bring it up. GOOD DAY SIR!
Off topic: Also, Spartan ops is awesome and I hope they continue it, despite the games falling popularity 
Your opinions Please!
(I am Noob, correct me If wrong)
PEACE 