This is from the manga Kaiji. A hated character is making his departure, and Kaiji thinks to himself, "消えろ！消えろ！。。。！” ”せいせいすらあ。。。。”
The first part is pretty easy, basically like "Yeah, get outta here!" But I can't figure out at all what the ”せいせいすらあ" means. There's tons of meanings for せいせい、and not having much like finding info in すらあ either.
Any help is appreciated.