If he’s of an obsessive mindset, latches onto a thing and won’t let go, the very best thing IMO is to get him into some kind of sport or game, chess maybe if he’s very much in his head, or something subtle like that which will compel him to live in order to achieve mastery and which helps him take a step towards grounding himself.
There are many games like that if sports aren’t viable, from Go to poker, if you can get him hooked those might give him a reason to stick around.
That aside, and assuming he’s getting psych help as needed because as @DarkestKnight says that has to come first, I’m going to share something, slightly edited, that I posted to a guy earlier that may also give your friend a place to go if he goes from RHP renunciation (“something wrong with life”) ideas, through the mangler of psych treatment, and then still wants to mess with the source code of reality afterwards (something ill-advised IMO):
(Magick is innately destabilising) but you can still affect your reality and get a bonus of learning to control your own mind better if you study the Science of Mind, because it has (arguably) the same foundations as the work we do here.This kind of magick is also the type with which I personally have had the most consistent results, over time, and I use it as a foundation for all my other work - so it’s not 2nd best.
If you search online and at archive,org for works by the authors Napoleon Hill, W. Clement Stone, and Wallace T. Wattles, you’ll find some of the key texts, they’re often out of copyright as well so you can find PDFs and audiobooks that are legal to download.
There are many works created later that are by other authors and derivative, but the originals have more power.
These all seem legit out of copyright, as far as I could discover:
I really think he’sd best leaving it all alone for a while, but if suffering in the world, for any group or person other than himself still bothers him, you may be able to pursuade him to “stay” and become like a Boddhsattva and use his power to help others, that MAY assist with the metaphysical reasons he’s trying to leave this plane, but obviously, not a doctor here so he needs psych help first and foremost.
As the link @Dinmiatus shared above showed, I found RHP concepts of transcending this “lower” and “flawed” reality piled on top of pre-existing innate depression and suicidal tendencies to be a toxic mix, I posted how rejecting that assisted me in this: