I don't think it's impossible

As Shelia said to Bonnie, Expression is a manifestation of a person’s will if they want to then they can do virtually anything they want. So yes, someone with expression can kill Hope, regardless of her regenerative abilities and vampiric side. Someone with very powerful dark magic could kill Hope too, however, she would probably come back to life or they would find a way to prevent that from happening by destroying her body.

if she was going to come back to life, why was Ryan so devoted to killing her? that's not kind of stupid, sorry. she could come back as a tribe, for example, and become even more powerful, unless someone with the expression "blocked" that side of her like Esther did with the werewolf side of Niklaus and Keelin did something similar.

Ryan probably didn’t know that she would come back to life.

Not that related, but i’m kind of nit picky. Keelin used science, not magic, to keep her werewolf side dormant

Cant tell if your being sarcastic, but keelin said she treated it medical issue and not a magic one.

I know that Keelin used science, not magic. I just think that if she managed to damage her own species, her body, her mutation without using a drop of magic, they could do the same with hope. as several characters say: nothing is truly immortal, which is quite true.