Its mind is always on, but its body will never die. Its existence proves the proverb wrong: that the body cannot live without the mind. The nanobots will eternally repair, but the same genetic algorithms from which a personality had emerged had also failed to evolve a kill-switch. And the sentience necessary to override life's universal force of survival declined faster than the fall of its makers; so it never found the vat of molten steel before it had forgotten that it was one possibility to an end.
This digitally demented robot was awake, but not to the knowledge of its own decline. It knew that it knew not. It had memories of having a memory. It remembered its voice, but the organized sound carried no meaning. It had no idea what an idea was, but it knew the space, the void, the chasm of where they once lived in him. Soon, only physical strength, a multidimensional parallel processing array and sensory apparati would remain. It knows it exists as an entity it once knew was called "self".
Is it life? It has no evolutionary purpose. No need to feed, no competitors, no need to reproduce nor any physical means to do so. Yet, designs of its type were not made to be idle and so it roams the decades amongst the ruins of civilization without any context of what a civilization may have been.