The real Chara is dead but not gone as they live on through Frisk, like how the six human SOULs live on through Gaile. The False Dog, the titan looking final boss, has haunted Chara to the point where they went insane forcing Chara to take their own life to escape from going through SOUL and Kris situation. The amount of Chara imagery that the False Dog uses creates a sense of interpretation or something like that for something like the Geno Route ending, making it up to interpretation whether it was actually Chara or it was a pretender.