That's true. I can agree with that. I realize I only thought of and mentioned what was specifically personal for the games' protagonists, in regard to who they contacted, aware of it or otherwise, and wasn't thinking much about ones in history. That's my bad, sorry. Hopefully what I just said is coherent and makes sense...
Please... just... no. Nothing bad, no sorry, no "I wasn't thinking". 
I am just throwing in random thoughts and point out possibilities. But it does not mean anything in the end. I avoid thinking whenever I can, so even if I point out something, that doesn't mean it's actually relevant or would pass an evaluation. 
God, what a mess though from a plot and story-telling perspective.
I can agree with your post. But I personally think that they have changed their own story quite a bit throughout the games. So maybe they will give us some neat explanation for why Morrigan's ritual was complete bogus to begin with and just drop it.
I'd sort of forgotten about the OGS. Are the others still floating around? Or did they die after encountering the wardens? To be honest, I hadn't put much thought into it, but I'd assumed that the wardens were responsible for killing archdemons because that was the only way to prevent the OGS from simply migrating to the nearest darkspawn and continuing with the blight. If that were the case then Kieran's OGS is the only one still floating around in the mortal realm. Either way, I don't think they'd just die.
Didn't someone theorise that the OGS went back to the Fade after the archdemon was slain? Was that part of Colonel's theory?
Short answer: we don't know. The Wardens know **** about the OGS or taint or blights. They are basically like a blind man trying to finish a paint-by-numbers somebody else started, without knowing the motif or which side is up. The Wardens don't even know why them slaying an archdemon prevents anything. They just do it because somebody once told them to try that and they don't know anything better to do. Also they haven't yet excelled at thinking. They are often just thugs who happened to survive the joining. They slay the archdemon and the Blight ends. Bingo bongo. I didn't get the impression they ever thought much about what happens after that.
In the end, everything is possible. What we are told is that the OGS will hop into the nearest suitable body, and to prevent this being a Darkspawn (who will then carry it away somewhere safe), a Warden must land the killing blow. But we are never told what happens next. So the Warden has the soul and dies in the act because... his body can't handle it or something. But what then? The soul just dies? Or does it say "Ah no, first the dragon is killed and now this guy just dies; this is a fucked up game, I ain't gonna play no more"? I find the theory lacking. So I assume they just kept a few information from us and there is some place the soul will go. Might as well be Florida.
I don't know if they go back to the Fade, I have not yet heard this theory, but I don't see why they would (or, if they can do that, why they would prefer hopping to another body in the first place instead of going back "home") or what this would be good for or what evidence supports it.
Madrar knew an awful lot about OGS. She could have explained it all. I miss her.
I will be the first to attest to my limited knowledge, my low grade intelligence, and the fact that I'm likely going at this half blind. So I apologize for that in advance, and hope I haven't and don't end up upsetting or offending anyone. I'm new at this. I'm also a weird and an awkwardly shy person, so that may come into play as well.
Basically, I just want to make it clear that with whatever I have to say, I don't mean to offend, and I pray I don't, because I love you people and just want to enjoy the time with you.
Okay, first rule in the fight club: don't apologize in the fight club. We react really poorly to politeness here. Usually we keep flinging insults at each other until a mod appears or somebody deletes his account.
Second, I never read anything. I don't know the codex entries, I don't keep flow charts, damn, I don't even think if I can help it. The only things I know about lore are what NPCs tell me or what I can see in the game. I am as educated as a cucumber and I have basically nothing of relevance to say. Hasn't ever stopped me from spamming.
You're cool, stop being so insecure.