Sure they COULD but they wouldn't because doing that would be poison for that team, Look at the NBA star players demand trades all the time and they eventually get it almost every time.
Contracts in pro sports don't mean ****, especially when it comes to superstar players, all they are good for is assuring the player gets paid.
If a player like Mcdavid or Matthews or Eichel says "I want a trade." they are either A going to get it o
Or B the team will do ANYTHING to get them to change their mind because when you are the face of the franchise, and in Mcdavid's case the face of the league he hold the power, if he demand he's getting traded OR the Oilers will do whatever they are told to keep him happy.
Mcdavid is the face of the Oilers, AND the NHL.
Like it or not, Mcdavid is the boss, Mcdavid calls the shots