Somebody - maybe N.I.D. - want to take out Jack - maybe revenge. They inject him with that drug from the… which made the injected person younger and delete their memories. They didn't want to kill him - maybe in a hope they will be able to use him in the future: the ancient gene or knowledge or black mail material…. But Jack didn't lost his skills - fighting, maybe technical skills - he managed to escape, and try to hid in one of the bigger city with his kidnapper after him. His half brother or cousin MacGyver get a message from the Air Force that Jack died or went M.I.A. or something. He start to investigation, he maybe snake in the SGC and meet with Jack's team or Hammond.
One of the missions went wrong and Jack was left behind. He was hit by a Jaffa's staff weapon and was pursuit died. A God of plays or games captured him. The god has an arena and he force his prisoners to fight for life or death. There could be free warriors as well who want to try themselves out or to prove their worth. Jack becomes the Champion but he didn't want to fight. Maybe he save some kids life and the god black mail him with the child or other children life. - The story could be slash, mpreg, het or gen. DE-age if the champion's reward is the youth. The team won't come across him for years, for example some Toak'ra mission the gate to this world. Will they recognize him, How they will react? Will they able to rescue him and his ward/family.
Daniel touch something he shouldn't and Jack pay for it. MPREG, Slash - Jack has a lover, and when Daniel touch something a beam hit him -maybe de-aged - and after sometime he became pregnant with his lover child. Maybe it vitalize his ancient powers and it caused his pregnancy. Maybe de-aged, and ancient gene when Daniel touch something a beam hit Jack which vitalize his ancient powers.
The team gate in the world where legal the slavery. The ruleres of the planet -the owners have blue eyes, and usually blond or light brown hair. When the native find them they believe that Daniel was one of the rulers and Sam is his sister or wife, while Teal'c is his body guarded. And because every master has a sex slave as well.. his role was left to Jack. Maybe the ruler like to have Jack in his bed
Slash - episode Need - I always thought Daniel was so far gone he wouldn't have know what he dose in the end and hurt his friend (Jack). But fiscally and sexually.
Slash - episode Need - the time in the mine was not pretty, they needed to went thought some hard ship to leave thought, the other prisoners as well the guards.
While both the Jaffa and the Toak'ra on the alpha site, jack got a message he was withdraw from his position as 2IC of SGC. The new man is his old black ops CO who now a General. They have a bad past? What will it cause to Jack? Jack will be called back to a newly formed black ops team which will haunt down the Goaulds. - maybe de-aged by the drug without the memory loss.