Reportedly, the McDonagh trade is just the opening move for Trotz this offseason. According to several sources, the move was intended to free up cap space so that he can pursue a 'high-end scorer' either in free agency or on the trade market. Notably, Trotz did joke that Marner is not a free agent, but that does not mean the Predators won't be in on him when the Leafs inevitably put him on the trade market.
All of that being said, Marner does have a full no-trade clause in his contract. If he does not want to play in Nashville for whatever reason, he won't have to. We will just have to wait and see what the summer has in store for us.