Be warned that you can very easily snap one of the smd led's that are on the circuit in the middle, which would destroy the whole thing in the process. If a liquid spill is the cause, it would have to be some kind of opaque liquid (milk, coffee, etc.), and you could try to take the whole backlighting sheet-assembly off the keyboard. (Though I can't imagine how it would have gotten there in the first place) You could try turning your laptop upside down and flushing whatever debris might be stuck under the keyboard with a can of compressed air. So it would seem that the thin sheet of polycarbonate that diffuses the light and spreads it across the whole keyboard has either gotten misaligned with the side-emitting led's, or, something is blocking the light from the led's from entering the medium.
The led's behind the keyboard are wired in series, so the circuit itself seems to be fine.
You're getting light, so your backlight is working.
