Is it considered suicide if a patient with a malignant disease refuses to amputate or remove an infected organ—if death is the inevitable result of inaction—and is he sinful for saying that death is better than living disfigured?

If an illness leads to death and can only be removed by amputating the affected limb, then its amputation is obligatory; otherwise, it would be a form of suicide. If an injured person allows their wound to bleed until they die, they are disobedient to Allah Almighty and a killer of themselves. The decaying or diseased limb must be amputated if its retention poses a danger to life; otherwise, not. As for medical treatment in general, its ruling varies between permissibility, recommendability, and obligation, and it may be obligatory if it preserves life from perishing.