9. What Did The Teenage Jack O'Neill Clone Grow Up To Do?
In the seventh season, a rogue Asgard named Loki is revealed to have been experimenting on humans for almost twenty years. This comes to light when a teenage version of Jack O'Neill arrives at the SGC, believing himself to be the real O'Neill, even if no one else believes him.
It takes some time (and a lot of comedic proofs) but it is discovered that he is a clone of O'Neill, though one who has not been given the correct sequencing, meaning that he is dying. He may have days but, at most, weeks left to live.
After the discovery of Loki, the other Asgard (in the form of Thor) agree he must stop his experiments and also manages to fix the clones DNA.
That leaves and ending where the clone O'Neill goes back to high school, though with 30 years of military training and experience in his mind. Another Jack O'Neill running around out there would be a plot thread that should at least be checked up on, if nothing else!