Yup.
Only way he isn't on our cap next season is if he agrees to go on LTIR (At 39 turning 40, and 21 seasons playing in the NHL, I'm sure there's something the Leafs doctor can say prevents him from playing, chronic sore back or something
) or if San Jose loses Karlsson, has extra cap room, and decides to bring him in for another year, and I think even if they lose Karlsson, which I doubt happens to begin with, I doubt they would bring Marleau in.
He can only be bought out buy another team during the first buyout period, which is before his bonus is paid, so unless there is a team willing to pay 4.5M to get a 6.25M cap hit for the year after the buyout, that isn't an option.
So to me, he's either on the Island, or on the cap.