It is possible to recover from mental illnesses but not all mental illness fully disappear. The severity of the condition, seeking for help on time and sticking to recommended treatment options determine the recovery of someone with mental illness.
For conditions that cannot be completed treated but can be properly managed, it is advice that any time a trigger comes up, the affected individual should seek for help.
It should be remembered that being cured from mental illness is not always plausible. You do have the power to move on from your mental illness. For example, people who are suffering from depression may not be completely cured of depression. A time will come when there may be triggers that will make them become depressed again. Still, they can move forward.
They can acknowledge the mental illness that they had and just accept it as a part of their lives. The more that people deny that they have gone through mental illness, the harder it will be for them to recover. The journey to recovery is not going to be easy. Some will have fallbacks from time to time but it is possible.