I suppose, Russ, it would depend on how seriously the present bridge was weakened. If the heat produced cracking, for example, it may be prudent to not put anything at all on the present structure. Remember: Safety First!
Regarding the Loop trestle, it took that entire summer to erect the prefabricated pieces--not counting engineering and fabrication work that was done beforehand. I know--I was there every weekend that summer to photo-document the erecting process. An entirely new bridge at Lobato would not be simple, easy, or quick.
BTW, the Loop trestle was so carefully engineered and installed that when the last panel was lifted into place, bolt holes lined up perfectly and no shifting of already-assembled components was required. Amazing what we Americans can accomplish when we put our minds to it!
Mike