Oh goodness, thats interesting 8D Thank you
It does not prove it, you even see flowey at the very end, the video is incorrect, you should think for yourself rather than blindly trusting someone without doing any research yourself.
Well, that's your opinion.
not really since again flowey is shown to be still around at the end
If that is post credits, then that is up to individual interpretation, after that I refuse to think anything but Asriel still around just hurting and in need of healing.