Cleaned up liquid spill, power button not working

I'm working on a Macbook Air 13" that had a slight liquid spill. I cleaned it up and the computer will turn on if i short the solder power connections or unplug the battery and plug in the charger.

The power button does not work.

All other keys work fine.

Is this something that can be fixed without replacing the expensive top case (or motherboard, which I hope is not the case since all else works fine).

I'm very comfortable disassembling the laptop, just want to know why that one button would fail and not the others? Is it on a separate type of circuitry? Thanks!