But faking her death (and even the type of death) doesn’t really match the rest of the story. There’s no obvious reason not to return her after he thought Voldemort was gone, or at least to let Lucius know what happened in case she’s alive and didn’t want to return—which is unlikely, we had no indication that she was really unhappy or didn’t wish to be a part of her son’s life—or if she died in some much-less-objectionable way (he could give Lucius the memory).

Not doing this led to the last ten years being rather complicated due to Lucius’ enmity; Dumbledore mentions to Harry he’s quite constrained in his political actions. Eliezer also seems to write his stories such that serious actions have serious consequences.

None of it proof, of course, just strong evidence IMO that she really is dead and either Dumbledore or an ally he’s protected did it.