The abandonment Lyon Mt. to Plumadore in '46 is correct. Just an add-on bit of info:
In 1940, The D&H made a connection with the NYC at the new location which became Plumadore. The two RR's were literally feet from each other, so building a cross-over to the Central was as easy as could be. From there into Saranac Lake, The D&H abandoned their first piece of the old Chateguay Railway, and obtained trackage rights from the new connection down into Lake Clear Jct., and then up the Saranac Branch to Saranac Lake.
Hope this fills in any blanks...
As for restoring the middle of the line.....if only they would start running SOME kind of freight service to the north end, they could at least have some more money coming in, but that's a subject for another whole thread. (And yes...I know....the track has to be fixed before it can be used that way...but you get my idea.)