at the rate it's going it might just get to #1. it's been playing on radio non-stop for weeks now and the Grammys helped it lots, after this week i wouldn't be surprised if it just went from below the top 10/20 right to #1 on Billboard.
not sure if this was AP here, but "Stay" sold 65,000 last week (including the Grammy spike on Sunday night). Expect this number to rise significantly for next week's chart.