I'm sure that BNSF would snap up the Feather River Canyon from UP if UP decided to abandon it. They need it for their north-south route. Maybe not the line to Portola but at least Keddie to Sacramento.

A question about the burning bridges; if the vegetation below them had been kept low, as in small brush and weeds as opposed to having trees under them, would the bridges/trestles have still caught fire? There would still be a lot of fire nearby but not having it directly below the structure could have made a difference. Looking at historic pictures of the different structures you don't see trees below them. It looks cleared out.