I went back to see Asriel after I finished the True Pacifist run, and he talked to me. He told me not to trust Flowey if I ever see him again, and it left me wondering. Do you see Flowey again if you backtrack once more to the beginning room of the game? Or is it just the golden Flowers?
If you backtrack to the beginning of the Ruins again after already talking to Asriel, he will not be there.
However, you will get a nice picture of the Golden Flowers, which (presumably) includes Asriel/Flowey again.