Matheson has 39 pts this year so far, tied with Dahlin and a few others for 8th amongst NHL D's. He's ,75 PPG, en route to a 60 pts season if no injuries. He's certainly the most valuable asset we have for a trade (with a prospect or 2/ picks). No doubt.
But the problem is: who's going to play 20+minutes and be the offense QB in the next few years? Hutson? It remains to be seen and if so, it wont happen next year or in 2 years.
My point is that we need a Matheson for the next 2 years to log those big minutes and carry offense duties. I assume he will be close to/over 50 pts per year. In 2 years, he will be 31 and still have a good trade value. So I would keep him until the 25-26 season.