Even if Wagner doesn't start producing, I suspect he'll have a spot on the Kings roster. He's one of the few remaining Kings forwards that bring the physical play (much needed with Clifford's departure), and his nightly breakaways frequently draw penalties. He'll have to make it out the other side of the expansion draft (The Athletic's expansion draft preview from earlier this month have him as the player that Seattle will take), but I can see him as the long term 4RW on this team.
His defensive play is still a little bit suspect, and he sometimes makes some poor decisions in his own zone, but if he can figure that stuff out, he'd be a good option for the PK as well. He and Kempe as a PK pair would significantly reduce the amount of time the defensemen have to set up in the zone.