The first half to next season might have its ups and downs, but I expect the tabs to be better in the second half, as Reinbacher gets his feet under him and he becomes able to keep up with Hutson.
Worst case scenario, Carrier pairs up with Guhle again for next year and we have more time to find the right candidate as our 2nd top-4 RHD.
In the first half of the season, Matheson, before being traded at the trade deadline, can play with Hutson again. Then Reinbacher can step in.
Habs need to address the 2C situation in the offseason, though.
Possible UFA options, if they make it to the UFA market:
Brock Nelson (NYI)
Mikael Granlund (DAL)
Matt Duchene (DAL)
Sam Bennett (FLA)
I omitted to add players like Tavares or marchand who would never play for Montreal, even if they did make it to the UFA market.