Some illnesses last a long time and can reduce a patient's awareness so that he no long... - Jurisprudential Answers - Book of Fasting

Ahmed al-Hasan Response:

The ruling on fasting is as explained above: if, for example, the illness continues for five years without recovery and he does not fast Ramadan during those years, he does not have to make up those fasts, but gives one mudd for each day. As for prayer, he must perform it in whatever way he can and in a manner suitable to his condition, or make it up if it is missed; it may also be made up on his behalf or charity may be given on his behalf after his death. Nor should the make-up on Laylat al-Qadr, which Allah has graciously granted us, be neglected.