A deal around Robertson for Kartye could make sense for both teams.
Kartye is a good 4LW with 3LW upside. He hits everything that moves and also has good, not great, underlying numbers. He scored 5 points in 10 games in his first playoff run for Seattle and scored 11G/9A this season. He is only 4 months older than Robertson so the Leafs aren't really getting older. Kartye also put up good, not great, results on the PK this year - the Leafs would be adding another NHL PK body in place of Robertson. Kartye can also play C. Realistically with Knies/Nylander/Domi/Marner/Cowan in the organization there isn't a role for Robertson in the top 6 anytime soon and he most likely is wasted on a 3rd line.
Seattle gets more goals which is their biggest need right now. They lose out on a solid defensive player.
This would only make sense for the current roster if Kampf is moved and Holmberg/Dewar play 3/4C.
Domi-Matthews-Nylander
Knies-Tavares-Marner
McMann-Holmberg-Jarnkrok
Kartye-Dewar-Reaves