Board Thread:Questions and Answers/@comment-30088034-20170306010427/@comment-13682699-20170309024102

It is highly likely that Chara COULD save but wasn't aware of it because they were never put into a situation where they would need it. (Monsters were more friendly at the time and humans are still far more determined by default) When they enacted the buttercup plan, they chose to die and not come back so that Asriel could use their soul, and they never had a fatal experience prior to that.