I certainly agree with you that he should obey God and live, but I don't think he would be eternally lost. He doesn't think so either.
Would you condone killing someone else because they brought shame to themselves, their loved ones or to God? I doubt it.
Suicide is the ultimate manipulative, passive-aggressive ego-trip. Anyone contemplating it should have no illusions they are doing it for some "greater good." Suicide scars everyone left behind. It is a selfish act of unbearable cruelty.
Your friend should find a minister or a competent therapist who can help him get through this moment of terror. It is only temporary. Anyone who doubts that has not lived long enough to know that nothing lasts forever but God.
What a gamble! What high stakes!
There is no promise in scripture that I can see that backs this up.
Paul