A question first person narration faces is: how is the MC telling his story?
Is he writing it down for some reason?
Is she orally telling the story to someone?
Mode of communication uncertain: first person approaching third person in its freedom from an explicit mode. I suppose you could imagine that the first person MC is experiencing the story moment to moment or recounting it in his own mind.
If your conceit is that the MC is writing down or speaking his story, then it will be unrealistic to go beyond the moments BEFORE suicide. You could go right up to his decision to commit suicide, his declaration that he's about to kill himself, but without a postscript in another POV, the reader won't be certain he went through with it.
In the "third person" first person, the MC could go up to the moment of death, even beyond it. Some readers won't buy this, but many others will have assimilated the convention that such narration is, yeah, real-world-impossible but story-world-acceptable.