He simply needs to get stronger, there's no way around it. To become the player and leader the Canucks invested in, he must come back this summer in shape, more driven, and laser-focused.
Pettersson has already told reporters that his summer training will be a priority heading into the offseason. Weather he returns to Vancouver for the start of next season is beyond his control, but regardless, he needs to take this summer as an opportunity to reset and come back the player we all know he's capable of being.