Absolutely, everything is predetermined according to the divine Knowledge and Wisdom. Nothing happens in this world except that which is already recorded in the Heavenly writ called al-Lawh al-Mahfuz.
As for refusing marriage because of being sick or having some disability, either mentally or physically, this cannot be given a general rule as it depends on the nature of the sickness and its effect on the marital life and also on one’s need for marriage and whether he or she can dispense with it.