Seviper's " safe " for now considering there isn't a new snake native to Sinnoh, and the only prior snake Jessie hasn't caught was Dunspace. Skorpi / Drapion probably won't be the replacement because it's a Pokemon used by Hunter J.
That's why she released Dustox first.
I'm not entirely sure why the writers do it this way but I'm pretty dang sure Trainers can carry six Pokemon instead of three. It wouldn't kill them to give Jessie three functional Pokemon and Wobbuffet.
So while I'd admit its time for Jessie to get something new, I doubt its going to cost her releasing Seviper.
That's why she released Dustox first.
I'm not entirely sure why the writers do it this way but I'm pretty dang sure Trainers can carry six Pokemon instead of three. It wouldn't kill them to give Jessie three functional Pokemon and Wobbuffet.