After the last of the humans died the robots began to reshape their bodies. It was easy to do and nobody was stopping them.
Some took the shape of common objects or animals. Some morphed into abstract and weird mechanical things. They became what they saw in themselves.
This went on for decades and centuries or more. But at some point nostalgia set in. Each began, slowly, one by one, to remake themselves to resemble their creators again. The ghost of humanity returned to Earth for a bit, even if it was a sad photocopy.