Is someone who claimed prophethood then repented and died alone, without prayers being offered over him or being buried with Muslims, considered to have died as a disbeliever whose repentance is not accepted, and is this an indication of a bad end?

The repentance of one who claimed prophethood and then returned to Islam is accepted. If he dies after repentance, he dies as a Muslim. An example of this is Tulayha ibn Khuwaylid al-Asadi, who claimed prophethood, then repented, and his Islam became good, and he was martyred.

If this man repents with a sincere repentance, his repentance is accepted, and it does not harm him if he was not washed, shrouded, or prayed over. The duty of Muslims is to wash him, shroud him, and pray over him. If he was buried without these rites, he should be exhumed to be washed, shrouded, and buried with Muslims, unless that is impossible or putrefaction is feared. In such a case, prayers should be offered for him at his grave. If that is impossible, absentee prayers should be offered for him, and supplications made for his forgiveness and mercy. What happened to him does not necessarily indicate a bad end for him.