Ajay0, please do not use the "S" word. A better choice is life termination. I know, - a rose is a rose.... but the "S" word carries certain negative connotations. When a person chooses to terminate their life as a result of extreme suffering through medical conditions the process of karma does not apply, unless that person has a very low self worth.
There is a spiritual process called Sallekhana in Jainism and Prayopavesa in Hinduism wherein a person disabled by extreme senility or very poor health conditions due to disease commits suicide by fasting. This is only allowed only in cases of terminal disease or great disability especially in old age.
This is allowed because a healthy body is needed for performing one's material and spiritual duties. If the person is diseased his duty then is to restore his health through all means possible. If however this proves to be impossible, especially due to old age, the person does not incur karma by committing suicide by fasting. Such a death is also a spiritual austerity in itself adding merit due to the self-restraint and self-discipline involved in denial of bodily comforts and endurance.
However the young and healthy are not supposed to commit suicide as that would be tantamount to cowardice which is considered a sin. It is only the elderly and terminally diseased in a critically weakened state who can perform sallekhan/prayopavesa.
Those who are suffering from mental illhealth or depression should strive to gain their mental health back through practice of mindfulness, virtue and approved practices. This is their duty and willfully escaping from one's duty due to cowardice is considered sinful.
It is perhaps not possible for a person who has worthiness to terminate there life, why would a person who values their life terminate it? A person who has a very low self worth entertains thoughts of life terminate almost every day.
When a healthy minded person has a cancer tumor that is pushing against their spinal cord and endures unbearable pain the only remedy for relief is to use morphine. In that case the brain is virtually dead, only the body sustains itself.
Endurance of pain equanimously is a spiritual austerity in itself. I know of cancer patients undergoing surgery who did so practicing meditation or vipassana. This enabled them to endure the rigors of surgery and treatment better and gain spiritual merit in the process.
Generally in most religions, patient endurance of disease or ill-health is said to be meritorious and wipes out negative karma.
As a Buddhist, condemnation to Hell doesn't apply since Hell doesn't exist. But to a grown person who is a "born again Christian" it does apply. So how would the Buddha respond?
Hellish worlds has been described in Buddhism. Imo, the state of your mind, strong or weak, positive or negative, attracts similar circumstances after death.
However unlike Christianity, these hellish conditions are of a temporary nature and not permanent. You are only sowing what you reap, and no one has sowed infinite bad karma to reap eternal hell.
If a person can die mindfully, it is considered to be very auspicious and meritorious. But most people become unconscious then mainly due to fearful imagination and terror of death. Steady and diligent practice of mindfulness can enable a person to be mindful to the very end and even in death.
Death is considered to be a very beautiful process when it is experienced mindfully.