The Leafs actually have to expose two 40/70, under contract for next year forwards.
"Two forwards who are a) under contract in 2017-18 and b) played in 40 or more NHL games the prior season OR played in 70 or more NHL games in the prior two seasons."
Fehr could be one of them, but they need another. Capfriendly.com has a tool which shows the possibilities
https://www.capfriendly.com/expansion-draft. Right now, it looks as if that would have to expose Komarov or Martin. They are too valuable to lose in that way.
I think that the potential to use Fehr as one of the forwards to be exposed is clearly a big plus for this trade. (An aside: has Tim Chiasson at Editor in Leaf, who has been slagging this trade actually read the rules?) The point is not so much that Las Vegas would take Fehr. It is that having him makes it unnecessary to expose someone else the Leafs might regret losing.
A second point, IMO, is that it would still be useful to do what is necessary to make Smith eligible for that second slot, namely play him one more game and sign him to a cheap contract for next year.