Talk:Alphys/@comment-82.40.130.37-20151027025047/@comment-118.200.11.210-20151115101050

It's presumably suicide, supported by Alphys's character showing symptoms of depression. She tends to say self-deprecating things, has little confidence in herself, and as revealed in the True Pacifist route, she's been silently blaming herself for all her failed experiments and has been suffering under the weight of her lies. Also, in her Lost Soul form, she mentions her fear that you/her friends hate her, which is very common in depression (projecting self-loathing). When you add it all up, suicide becomes a very probable reason for her disappearance, despite how heartbreaking the idea is.