I've been a fan of Jazz since the second game came out, so I've thought about this for years. And, when you consider the fact that the Jazz canon is pretty bare bones after Jazz 1, my headcanon is very in-depth...

The entirety of JJA was a drug-induced dream that was actually a failed assassination attempt(Kind of like the Matrix meets Inception, except heavily inspired by Star Wars and set inside Jazz's mind). The villain who set this all up is the turtle from the JJ1 comic, who put himself in the dream and became Dark Shell. After the dream, Jazz imprisons the turtle and uses information from him to track down Devan. So then, after a while, Jazz cryogenically freezes Devan(Since he would break out of prison, and killing him would make him a martyr, and plus he might be useful in the future). So then, Jazz spends most of the rest of his life as a family man ruling Carrotus.

There is more, but what I've put above only about half of Jazz's story(Less if you count details I skipped/skimmed over), and then there's Spaz, Lori, and the rest of Devan, so we're talking walls of text here(Maybe I'll post something in the War Tavern at some point).