At 40 years and 5 months his form is unlikely to ever return. That said, he absolutely should go to the Ardennes. They suit his diminished skillset better than any other race.
If he doesn't have the form to win LBL he's not going. He basically said this before the season restarted. His comment was after the Tour his schedule was Worlds maybe LBL then Vuelta. He flat out said he would have to have the form to win LBL or he wasn't going to the Ardennes. He's not missing la Vuelta. He doesn't have close to the form needed to win LBL, so there's no way he'll go to it and instead go home and get ready for la Vuelta.