What is the ruling on one whom Allah has taken in death following a severe illness that prevented him from praying due to his inability to purify himself, and is there any sin upon him for that?

Prayer does not fall away from the sane, adult individual, and he must purify himself according to his ability. If he is unable, purification falls away from him. He must pray in any case, so he should nod with his head; if he is unable, he should motion with his eyes; if he is unable, he should perform the actions of prayer in his heart. The deceased's father erred by abandoning prayer, and we ask Allah to forgive him. Supplication should be made for him and charity given on his behalf. According to the majority of scholars, it is not permissible to make up prayers on his behalf. However, some scholars, such as Ibn Abd al-Hakam from the Malikis, permitted hiring someone to pray on his behalf for the prayers he missed, but there is no evidence for this opinion.