It is religiously unlawful for a person to kill himself, it is an assassination. He would thus go to the Sight of God as a murderer who did not repent. That is not acceptable.
Committing suicide is a form of murder. One who kills another would remain in the Hell for all eternity. The verse about this is very explicit in the Qur'an. That person would die without repenting, that is because he would thus be taking the life God gave him. And by killing himself he would be losing all he has, while it was possible for him to survive and continue his struggle in the way of God.