Well, I'm guessing Sarah will eventually go back to the Labyrinth, hopefully by volume three.
Jareth's visit will have her concerned, as she will soon find out what has happned to Toby, and will want to see for herself if he's okay.
Since I won't know what happens for quite a while, I'd like to speculate.
1. Jareth will take her back somehow, since he has the ability to leave his world in the first place.
2. There will be some type of portal Jareth will open.
3. Jareth will be able to commincate with Toby somehow, and will ask him for help.
4. Toby will come to see Sarah, and find her in the company of Jareth. He will invite them both to come back for a visit.

Jareth's visit will have her concerned, as she will soon find out what has happned to Toby, and will want to see for herself if he's okay.
Since I won't know what happens for quite a while, I'd like to speculate.
1. Jareth will take her back somehow, since he has the ability to leave his world in the first place.
2. There will be some type of portal Jareth will open.
3. Jareth will be able to commincate with Toby somehow, and will ask him for help.
4. Toby will come to see Sarah, and find her in the company of Jareth. He will invite them both to come back for a visit.