I don't know the answer about who originally created this lovely artwork. One thing to consider, though, is that sometimes when an author or artist deletes, orphans, or otherwise withdraws their online content, it's because something has happened in their real life that makes it awkward for them to have their name associated with a searchable, public work (maybe they got doxxed, maybe an employer is searching online and they aren't comfortable with their fandom creations being visibly associated with them in that context, maybe they are not out and don't want to be outed accidentally because someone in their life has come across their pseudonym, maybe their feelings about a fandom have changed and they just want to leave it behind, etc.) So, although in general I think trying to give credit is important, if the creator has deliberately dissociated their name from their work then I think, since we don't know their reasons, it's better to be cautious and not add their name back onto it. Both giving credit and respecting deletion/dissociation are about respecting the creator, so I think which one is the best course depends on the individual case.

Of course, sometimes an artist's name gets dissociated from their work against their will, due to reblogs that don't give proper credit, and that's a case where searching for the original artist makes perfect sense! But from what you've said, that doesn't sound like what seems to have happened with this blog.