I'd put the chances pretty low of a trade. There are simply way too many checkmarks the trade has to fulfill.
1) Marner has to decide that it is in his best interest - he will want to benefit from this trade. IE a Willie type contact, plus, plus.
2) Treliving has to get good value for one of the most productive wingers in hockey. Outside of a couple of players, our farm system is shit and our near future draft picks options are shit, this is not a cap dump for future considerations.
3) The "new" team has to have NHL ready assets and cap space to sign Marner and probably be willing to sign him long term.
4) Probably fair to say the Leafs are not looking for a forward to replace Marner, the other team needs to have an elite Dman or an elite goalie, that they are willing to part with. Likely the Leafs want the player to be in his prime 25 to 29 years old. How many teams have two elite #1 Goalies they they are willing to part with? How many teams have good to very good dmen - probably Right side d-men - that they are willing to part with.
5) Every team knows the Leafs want to make changes, no team is going to help the Leafs, every team will offer pennies on the dollar for Mitch.
I think the core five will be back again next year, simply because no team will pay a reasonable price for Mitch.