I think people have misunderstood that panel, it doesn't speak of Shigaraki's hability to be saved, is about the huge hero complex that Deku has, he has an almost pathological need to save everyone which makes him the greatest hero but at the same time one with many flaws, Deku himself says that morally Shigaraki has no salvation and he hates him but he still wants to save him from AFO.
I believe that Shiggy will not be saved but he will achieve his own liberation by killing AFO and finding a purpose of his own.