It highly depends on when the Bows spawn. If they spawn while the disease is inactive and the fry can reach 2 inches or so, then they're in the clear. I've heard reports of the Bows in the Bow spawning year round, so there's hope.
They could also try to obtain some brood hens from the Bow and start stocking the Bow with fingerling size "wild" hatchery fish to maintain populations until naturally resistant members of the population can be left to breed.
More aggressively they could actually try to find genetically resistant trout from the Bow, breed them and then stock the genetically resistant fish into the Bow. Not sure that's realistic, but Colorado did a similar thing by stocking Hofer Bows into their watersheds. These are disease resistant trout from Germany. There are pros and cons with this approach. Check it out:
http://cpw.state.co.us/learn/Pages/W...eParasite.aspx