Some time after Jennifer return for Alice's funeral and then returned to London Jack disappeared. Jennifer returned alone in the late fall of 2010. Supposedly over the next few months Jack would send email that he was on a walkabout in Australia. He never talked with them or they him. Yet they believed that what was he was doing. The messages from him made it seem he no longer cared.

Jennifer eventually became involved with Dr. Dan Jonas, who had a propensity for dating his female patients. In a weird series of events a mad man stole Jennifer's heart, Dan and his daughter Molly put it back inside Jennifer on their own. Jennifer eventually divorced Jack in absentia. Dan and she became lovers during this time.

[In an attempt to revive the show's week ratings Ken Corday, Executive Producer, announced a show reboot. Producers and writers were let go, and actors fired during include Matthew, were rehired. Leading up to the big returns the show would air various short promos].

Thanks Jason47 for the following information:

Promos:
Air date August 24th, 2011: Jennifer looks over Jack's photo which is in the Horton living room.
Air date September 8th, 2011: Later what appears to be a cave, the person is obscured, but he is writing on a cave wall.
Air date September 14th, 2011: The third clip shows a man, chained inside a cave.

Full Episodes:
Air date September 21st, 2011: Jennifer is on a date with Dan at the Brady Pub they are about to go biking, Dan leaves and Jennifer checks her messages. The phone rings, it is "private." She answers it but no one responds. Caroline Brady wonders if everything is fine. Jennifer has a confused look. She tells her she is okay, but her phone rang and no one was there. Caroline tells her it was just probably a bad connection, or a wrong number; it always happens to her.  Jennifer tells Caroline that it bothers her when it happens, she gets the strangest feeling.

Meanwhile, a man wearing a turban talks to a man holding a phone, we only see his arm. The man in the turban, speaking in English but with a slight accent, tells the other man that he has spoken with the U.S. embassy and they have arranged a flight back home for him. The man turns his back, as the turbaned man walks off. The mystery man taps his phony nervously.

Air date September 22nd, 2011: Jennifer is in Dan's office and Molly his daughter is feeding him cupcakes. Jennifer's cell phone rings again. No one is there, she angrily tells the person on the other end, that whoever you are you are getting on my nerves.

We see the man again, holding a cell phone.  He is at an airport, there is an announcement in American accented English stating that flight 245 to Chicago is ready for boarding. The man, picks up his carry-on and gets up to the boarding gate, the sign on the door he passes through is in English and states only passengers are allowed beyond that point.

Dan wants to know who it is. She says it probably was just a bad connection. He is off to say good-bye to Carly. She tells him she will be there soon. She looks at her phone, and frowns, looking concerned.

Of course all the mystery man in the cave is Jack, for some reason he has been held in a cave somewhere, and  has recently been released, and is going home. Just as Jennifer has moved on with Dan.