I firmly believe that each soul contract has a set expiration date and that while free will, both our own and those we may come in contact with greatly affects how we live and how we die, I believe that spirit guides/guardian angels/souls of dearly departed/maybe even God itself will step in and prevent a suicide attempt from being successful if it's not our time to die, yet they can't heal the effects of the attempt on the person or their loved ones.

Predetermined date of death is a concept I write about from time to time, most comprehensively here with respect to suicide: https://medium.com/illumination/dizain-of-suicide-72bcde4dc8d8 If you don't want to dive into a 17-minute read (which despite its length is my most read and engaged with story), here's a compact version: https://medium.com/promptly-written/suicide-is-not-painless-ac4c0c999e81