Costs money to grade and lay track, plus you are altering the appearance of the area (is there earthwork to be done, trees to be cut?) and impacting the environment. How many trains would you have to run (if you get a net return after paying the running expenses - crew & fuel) to pay for all this work? I doubt the C&TS would want to expend the resources it would take to set this up when there is no reasonable expectation of success. They will need the money to fix/replace the bridge....
My 2 cents - If Lobato Bridge can not be quickly repaired, I would have it disassembled and carted away for a piece by piece replication/refurbishment. I would then find the best temporary solution to bridge the gap. Once the original is either refurbished, or a replica that meets modern standards is completed, I would have it erected during the off season to restore the original appearance to the site. This would get traffic going across the full line, and the funds for refurb/replication could be allocated over a period of time. This assumes that a temporary bridge could be built faster and much cheaper than fixing the old bridge though, which might be a bad assumption.