Why give up assets when you can just sign him in a year?
Because if the Leafs trade him anywhere but your team, there's a reasonable chance he's going to sign there.
How can any team be sure any player will sign with them in free agency. Your take is even more ridiculous then the one I previously commented on. Try and use a kettle logic and common sense when commenting.
Nothing is certain.... but you look at the history of most higher-end NHL players -- they don't often "pick their destination" based on factors other than money.
Even the money, it's usually more about what the money says (about how they are valued) than needing it in their bank accounts. Hockey players are conditioned from a very young age to not try to "pick destinations".
That's not to say Buffalo or Winnipeg or Ottawa are going to go into a potential deal believing that him signing is realistic.... but as long as it's a reasonably attractive destination, and they go in prepared to give AM the contract he feels he's worth, then they'll have a pretty good shot at signing him.