It all depends on exactly where the spill occurred and how deep in it got. And, the specific model Mac it is, which you haven't provided.
A few years back, a colleague spilt a bit of pure coffee, no milk or sugar, on the left corner of a Mid-2009 first-gen 13" Unibody MBP barely a few months old. Right where the MagSafe plugs in. It immediately blanked and shut down, would not start even after drying. Took it in as it was under warranty, and was told that a) the warranty was null and void, b) the logic board had shorted out and c) he would have to pay for the new logic board, around 50-60% the original cost of the unit. Which he would have to continue paying given the 18 month financing he had used for the purchase. I believe he managed to get the new board added to the financing.