From a reliable inside source that is only 75% halucinated, I have gained the full story of jazz and eva after the end-game cutscene breaks off.

When jazz and eva were just about to get married, jazz had an alergic reaction to Eva's lipstick and died. Eva, mildly shocked, changes her name to "Black Widow" and begins a carrer as an assassin. Lori moves to california for a year to get some serious plastic surgeory done, and spaz takes up smoking. One year later, jazz is rasied from the dead as a zombie. It is currently unknown who did it, but most signs point to a scientology cult that jazz was a member of at the time of his death. Meanwhile, spaz finds that he is out of cash, so he calls his ressurected brother and now not-ugly sister so they can do TSF in order to earn some much-needed cash.

QUOTED FROM A RECENT INTERVIEW WITH JAZZ:
(INTERVIEWER) So, I hear you just finished making a jazz2 expansion pack. Are there any comments you have on the outcome of it?
(JAZZ) I didn't get paid enough and my agent sucks.
(INTERVIEWER) How much DID you get paid?
(JAZZ) I got a can of beer and Arjan's bus pass.
(INTERVIEWER) I didn't quite get the plot of TSF. What is it about?
(JAZZ) Me, Spaz (my pet idiot) and Lori somehow teleport to haunted houses, cities and some freaky easter land. Then we shoot whatever is living there and steal their food and gems.
(INTERVIEWER) Is there a reason for doing that?
(JAZZ) Let me think.
(30 second pause)
(JAZZ) No.

After doing TSF, the three jackrabbits split up and never spoke to each other again. Jazz died of old age at 91, Spaz overdosed on drugs and dissapeared one morning in 2030, and Lori became an accountant and was later assisinated, possibly by Eva.