Opportunity is not so far (it's actually inside a crater nearby I think), but it'd take months to get to place, and there may not be enough scientific value in doing so just to see the charred remains of Schiaparelli. But who knows, it's so over it's expected mission life that maybe someone goes "f* it, let's go take a look".
Not necessarily. Schiaparelli used hydrazine for fuel, and if it smashed into the surface it seems to me that it's a reasonable assumption that the whole crash site is contaminated with it. Is that something we want to get all over the rover?
With a bit more Googling, it appears that hydrazine's lifetime in (Earth) atmosphere is measured in hours. I'm not sure what that would be on Mars, or if soaking into the soil there would increase its lifetime.
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".
Opportunity is very very far, yes technically it is close if you are thinking about traditional modes of transportation, but it traveled so far only about 40KM, and it's max speed is about 2 inches per second it is not going to get there.
