That streak was a classic CR. Depending on the angle of incidence on the CCD, you can see different shapes.
Depending on how hard it cratered, and how soon Opportunity could get there, it could be the most important thing for Opportunity to do.
It's a fun mental exercise, I guess -- I'd love to hear from somebody in the field who knew more about hydrazine -- but as the Opportunity rover is still a long (likely impossible) distance away from the crash site, it will likely just remain a mental exercise.
Months, to say the least -- the rover moves very slowly. Ever since it got to Mars, it's moved at about ~3,5 km/year (just shy over 2 miles/year). I think a more realistic estimate could be "longer than it has been there".