I actually did this, in a sense. I told all my friends that I planned to kill myself and disappeared. The end result was them being extremely hurt, and when I came back after my attempt failed, our friendship was irreparably destroyed- their trust had been broken, they were more upset that I left them without saying anything rather than that I tried to CTB. They could understand being suicidal, but not that their close friend could just leave them like that.
I have also isolated myself without giving them any reason why, and tried to ctb in secret, like you said.
People care about you. You disappearing won't change that. My personal opinion based on the aforementioned past experiences is that, you shouldn't leave. Your death will inevitably hurt them, but at least they will have happy memories of you that they can look back on. If you leave, on top of the pain of losing their friend to suicide, they will also feel the pain of not being by your side before your last moments.
Honestly, I wish I had never ever left them. Even though I am still alive, they feel like they lost their friend. When I kill myself, they will lose me permanently, but they really didn't need the additional pain that they felt while I was alive.
