The Upside Down is a world that people are not supposed to enter. Those who are brought there by Demogorgon are not meant to make it out alive. Yet, Stranger Things has shown that it is likely to make it out alive as long as you will be saved by your family members and friends. Some did not make it like Barb but there are also some who were able to do it well.
Since the show is starting to show more characters, it is very likely that there are more characters who will be inclined to enter the Upside Down for various reasons. Those who are avid viewers of the show can only guess what will happen next.