To see if your conclusion is based entirely on terrible logic or if you had insight/info into whether Marleau is purely mercenary or driven by pride/winning
I believe fans that think Marleau is suddenly going to retire and then Leafs deal his contract away to avoid a $6.3 mil cap hit to solve pending cap concerns are going to be disappointed.
Leafs have pending cap issues due to the pending upcoming large contracts, but I don't believe Marleau is going to willingly help resolve them.
Marleau accepted a Leafs 3-year deal, leaving his only/original team of 20 years and his 2 year contract offer on the table in hopes of winning a Cup.. Now that Leafs added JT the odds have improved significantly, and he suddenly pulls the plug on his NHL career to help the Leafs compete better using his cap space in year 3 for that benefit.. I'm personally not buying it, and baring injury or a significant drop in his own play this seems more fiction than fact.
If Marleau had any intention of retiring after this year he could just have stayed in SJ and played and ended his entire career there. Ironically SJ was more Cup competitive last year than the Leafs were, so Patty might already be having doubts about leaving in the first place.