re: If...
How long would it take NASA to send up another one?
2 months...?
Or would the Russians be able to do it sooner?
They build 2 Soyuzes per year and need at least 1 pilot , so there's only room for 2 and there are 7 astronauts to return back.
And for how long and how many extra people can the ISS support? I don't know, 10 persons.