Here's where I wish I had my old computer and the study I did on it!
Depression and suicide are threaded throughout the Bible. Never do you find a case where it is stated that suicides are unforgiven offenses. The only sin that the blood doesn't cover is rejection of the Holy Spirit...ie being an unbeliever.
I've heard people argue that there's not enough "time" after a suicide to be forgiven because you can't ask for forgiveness. That makes no sense. Christ died for sins past, present and future. It makes me angry to hear humans decide there are exceptions to that because there aren't. Over and over, God's word emphasizes grace and forgiveness to ALL believers. We are told that believers are SEALED. We were bought. We are owned. Forever. That is the promise. God's word says so and anything else is a lie.
The other argument I've heard is that committing such a sin is proof that one isn't a believer or they wouldn't have committed such a sin. My answer to that is a question. What sin is so trivial that it wouldn't have required Christ's death?
The answer is none. Sin is sin. Christ died as much for a little white lie as he did for serial murder. There wasn't more or less on the cross, it all resulted in Christ taking the same amount of humanity, the same amount of pain, the same amount of suffering, and just as much overcoming of death for our sakes.
So yeah. It isn't something that unseals you. And as far as questioning whether a person who committed suicide was mentally ill? Do people in good mental health do this? EVER? Even unplanned, such as Saul's armor bearer falling on his own sword when moments before he'd likely been fighting to save his own life, was plunged into an extreme state of mental distress.
So long as he was part of the family of Christ, he's home with his Savior, fully forgiven, all tears erased, and healed of any mental struggles he suffered from. No, it wasn't the most honorable way out of this life, but that doesn't change the fact that Christ's death ensures our eternal life after our death, however it may come about.