I think it comes down to how much the used rail is worth against the cost of digging the street up and repaving. I know lots of places where the crossing was left in the street but not even paved over. I also remember seeing Bay street in Toronto having the street car tracks paved over -- it seemed that they were just putting tar over the rails, not doing a full job. The rails resurfaced in a few years. I saw a crew in another street who had removed a couple of yards of girder rail from a line that had last run almost 20 years before. In the short run, it probably comes down to "who has to pay for it?"