It would be a logical, easy but still cool conclusion to Fain's plotline and the hunt of the Shadow for him: the "Dark One's hound" will be killed by the Darkhounds.

Fain was important for the plot in the past (e.g. for the Cleansing). But to use him yet again to manipulate some group seems a bit redundant with TG approaching and RJ's need to conclude most of the plotlines (which lead e.g. also to Masema's sudden death in TGS).