It is my prayer that he will reach salvation, but suicide is a sin. You cannot repent after death.
There are other things that go beyond mental illness. Was he possessed or just in a depression. As far as I know, suicide is still a sin. You are throwing away the life God gave you.
If you are basing your salvation on your work of repenting for every single sin then you are lost. Yes, repentance is a way of life, but our salvation is not dependent on how good we are at repenting.
You must base your salvation on Christ's righteousness, not your own work of repenting or not repenting. It is God who saves us...not our own awareness of whether or not what we are doing is sin.
We live in a state of grace. We are God’s even in suicide.
We don't know what was in his mind as he breathed his last. He could have repented of his action, though it was too late to do anything about it.
I am of the belief that those who decide to take their own lives are not working with their full faculties, therefore I don't believe God would damn them fully for their actions. I believe in the idea of Purgatory, because I believe in a Merciful God. Some, at death, are not in full communion with the Lord, and are not prepared to look upon Him in His Glory. We, who still live, are encouraged to pray for those who might be in that state, needing to be cleansed of some minor sins, or even some major ones for which they hadn't fully repented. We pray for them to be cleansed so that they can, at last, be welcomed into the sight of God, and be able to look on Him.