Eris is an unusual case because she has all the makings of a villain and if there's going to be a whole "hero-to-villain" swap trope used in Destiny, she's the most likely candidate. People use the events of the Dark Future to justify her inevitable fall, but that whole book only paints the picture following extremely specific circumstances that involve corruption from both Savathun herself and the Black Heart that wasn't destroyed in this timeline. Eris has spent substantial amounts of time amongst the Darkness and Hive both within the Hellmouth on Luna and the Pyramid occupied locations within the past year; but she's always held this sentiment of keeping her humanity intact. When she was dealing with the Phantasms of her lost fireteam, she resulted to maintaining the memories of the good times she had with them to dispel the Phantasms, and wrote letters about them addressing both Ikora and Queen Mara Sov as a way of documenting her thoughts and likely extending to a level of clearing her head (although that's not confirmed). She also did similar things during Season of Arrivals and Beyond Light regarding the messages from the Pyramid and regarding Stasis. She also kept close contact with her allies. During our attacks on Crota and the Taken War, she had the Vanguard to keep her grounded, as well as her alliance and loyalty to Mara Sov who considers her a trusted confidant. She also had Asher Mir who she wrote letters to before she re-emerged during Shadowkeep. Ikora was in close contact with her as well during this time, and with the arrival of the Pyramids, Drifter and Zavala kept her in close ties (as well as her continued support from Asher Mir and Ikora Rey). Obviously she now has ever closer ties to the colloquially named "Vandark" of whom aided her in utilising Stasis (even if she didn't learn it from them). We also know she's going to appear in The Witch Queen expansion based on the recent trailer alongside Ikora, a character who Eris has implied will keep her in a comfortable mindset. Point is, for all her exposure to the Darkness and with all her potential to fall to the Darkness and become an enemy, she's always had one foot on the side of Light. She walks the ever controversial "Grey Line" that Shin Malphur practises and even promotes, alongside her Vandark allies and even us. It will take a lot for her to fall to Darkness and become the enemy she rose to be in the Dark Future.