Dying in Limbo seems to take you back up to the previous dream level, without the need for a kick. The entire point of the movie is that when Cobb and Mal first encountered Limbo, they were unaware/unsure how to get out. They chose to stay inside until Cobb finally convinced Mal using inception that they should kill themselves together.
It's this method that Cobb and Mal use to exit Limbo and it's this method that Cobb and Saito use to leave Limbo at the end of the film:
Cobb turns to Ariadne, who is pointing Cobb’s gun.
COBB: What’re you doing?
She KICKS Fischer off the roof– AIMS again at Mal–
Fischer DROPS as the sky LIGHTS UP WITH ELECTRICITY– Fischer SCREAMS,
then GASPS, no longer falling, and we are– [in the next level up again]
COBB: Yes. And to take a leap of faith.
As Saito-san listens to Cobb, he looks at the GUN on the table between
COBB: Come back and we’ll be young men together again.