Unless Martin St-Louis changes how he constructs his defensive pairs and how he plays, I do not see things the same way I wold for other teams or Habs vintage.
I think Matheson stays with Montreal for the next two seasons.
I also think that Guhle will return to the left-side and anchor the 2nd pair.
Savard will be here until the trade deadline, with one of Mailloux/Barron/Reinbacher taking those minutes late in the season
This gives:
Matheson-Savard
Guhle-Barron/Mailloux/Reinbacher
I have not placed yet any of the other Ds, which will be fighting for a 3rd-pairing job:
Xhekaj-Struble-Harris-Kovacevic
The Habs could keep the four of them in a rotation. At least until the trade deadline. Patience is on the Habs side to sort this out.
If the Habs feel compelled to have an NHL-level top-4 RD, they could swing a trade for that player, especially if they plan on trading Savard at the deadline. It will be too expensive later in the season to fill two RD holes if Barron/Mailloux/Reinbacher are not NHL-ready by that time.
I would rather be patient with Barron/Mailloux/Reinbacher, I would even give Barron the 4D spot on the 2nd pair from the beginning of the season and suffer through his growing pains in the NHL. He would be buying the Habs time until their defensive prospects solidify their game, to then make a decision at the end of next season.