What is your advice and how can parents be persuaded to approve their daughter's marriage to a man who has recovered from cancer, knowing that they fear a relapse of the disease, while the girl believes in divine decree and destiny?

There is no harm in marrying someone who has recovered from cancer. In fact, it is permissible to marry someone who is currently afflicted with it, if the woman agrees. A righteous and religious suitor whom Allah has cured of an illness, and whose condition has stabilized according to medical reports, should not be rejected. This is in accordance with the Prophet's (peace be upon him) saying: "If someone whose religion and character you approve of proposes to you, then marry him. If you do not do so, there will be tribulation on earth and widespread corruption." If the parents insist on refusing, then be patient and find excuses for them.