I think the Leafs' roster is very much in transition and the coaching staff are deep in the process of separating the wheat from the chaff.
I think the top-four D of Rielly-Brodie and Muzzin-Holl is the most stable part of the roster.
After that, nothing is settled. Dermott will be exposed in the expansion draft and isn't getting much in the way of development. Lehtonen is an unknown quantity that can't yet be played in critical situations. Bogosian is a stop-gap with no upside, and Sandin is an ace in the hole with nothing but upside.
I wouldn't mind seeing more of Lehtonen-Dermott with Bogosian as a seventh D, and Sandin in reserve for addition to the roster in due course -- in case of injuries, or at worst after the expansion draft. His day will come.
The Andersen-Campbell situation is interesting too. Andersen is the most reliable goalie the Leafs have had in a while, but still needs to prove his worth as an aging, pending UFA. The answer next year could be either, both or neither of them, and I expect this year to be a year-long audition of the star and the understudy. Absent injury, I expect Andersen to get the bulk of the work with a good share to Campbell.
The forward group is almost too complex to comment on. Matthews, Tavares, Marner and Nylander are top-six fixtures. Hyman, Kerfoot and a few others are assured of long-term roster spots, depending on contract status. Thornton and Spezza are guest performers invited for cameo appearances. Mikheyev, Engvall, Brooks, Vesey and a few others are disposable parts that will be used according to their immediate utility. Simonds is the plumber who will be kept on staff until the leaks stop in the bump-and-grind department. Robertson is the golden-haired boy with a promising long-term future. But for the top-four and Robertson, everyone else is disposable and I wouldn't rule out any roster changes among that group. It is very fluid.