497 was put back into service because it was there. It had been left in Durango along with numerous freight cars because the Durango based engineer assigned for the second engine on the cleanup train which was the last Eastbound train out of Durango laid off.
The D&RGW refused to pay deadhead wages for an engineer from Alamosa to ride the bus, so they just used 498 and left 497 and about half the train in Durango.
When Bradshaw took ownership he set out to use 481, which was the last engine shopped in Alamosa, and hauled to Durango for eventual use on the Silverton. He also decided to restore 497 to service because it had simply been left there in servicable condition.