My N8 died. Just dead: no charging light, no vibrating after the power button was pressed, no nothing. None of the reset methods work (i.e. 8 sec power button). I'll take it back to 8ta tomorrow so that they can send it in. Unfortunately I have flashed it with a pre-release of Anna (though it was on the official Anna when it died), and a few weeks ago I have spilled some tea on it. So whether they'll claim that I voided my warranty is a 50/50 - probably depends on what the fault is.
Try taking it to Nokia Care point. They might give you a quicker answer. Although the 8ta route may give you a better chance of being able to get it done through warranty because those Nokia guys are real quick in pointing towards water damage.