If the reality is as you mentioned that your father loses his mind,
Salah is waived for him during the period of his absent-mindedness. If he comes back to his senses, he should offer Salah during that period as much as he is able to, for Allah (Glorified and Exalted be He) says:
So keep your duty to Allâh and fear Him as much as you can
As for the period during which he loses his mind, there is nothing due on him, because he is not held accountable for his deeds.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.