Jack Eichel
This should be a no-brainer given his importance to the Vegas Golden Knights. Numerous aspects show Jack Eichel makes the Golden Knights better, including the power play and forward production. Why would a team give away a player they acquired in 2021 to give them a franchise-defining center? It doesn't make much sense.
Sure, he might be a $10 million cap hit with two years remaining on his current deal. The Maple Leafs would want a young player who can be a complimentary piece to Auston Matthews. But cutting your nose off to spite your face doesn't end well. That's especially true when Eichel runs the offense well, making his teammates better. That's partly why they got Ivan Barbashev in the first place, giving him a great playmaker to compliment him.
On top of that, he's become a community staple, participating in numerous charitable causes in Las Vegas. He was even the captain for the Golden Knights in this year's Battle For Vegas, replacing Reilly Smith. When you get rid of a franchise-defining star like Eichel, it sets you back. Like William Karlsson, the former first-round pick would be a major loss for a team in a Stanley Cup window.