I recently had the same experience on my MBA A1370. Spilled liquid on the keyboard. I turned it upside down to remove the liquid and tried to dry with a little bit of heat from hairdryer. The first restart test ended up in only the fan spinning (I stopped it immediately with a long push on the on key). Second after trying to dry it was with half screen backlight blinking. I stopped it immediately too.
After a few days of rest, in order to dry it properly, the screen was back to normal but keys were acting like the ctrl key was always pressed (seen on keyboard display utility) however the trackpad was working fine. Everything was fine when using an external keyboard on USB.
Once I managed to find the right tools to open the case, I was able to check that LSI was red only on the back of lcd connector none anywhere else. I went to the case following the instruction but due to the rivets the keyboards layers are not accessible.
I asked some chinese friends to provide me the right naked keyboard for the aluminum case layout (big enter key was needed). I also asked some (+/-70) microscopic replacement screws (like the ones around the keyboard).
Once the keyboard arrived, I checked it by connecting it directly to the trackpad the setup was quite brittle but it proved the new keyboard was working normally. I had to pop out the 70 rivets. it can be done easily when all the philips screws around are removed. Just press the 4 keys around the rivet and it will pop-out. Some rivets heads were broken and I had to remove the remainder with a flat plier to start with a clean frame.
The new keyboard came easily in place, fitting exactly the frame. then the funny part of the job was to put back the screws in place of the rivets, checking that it was tight enough to have no play when keyboard was pushed slightly against the aluminium case.
Once the new keyboard was tight in place I put back all the stuff together and it was working as before the spill.
This operation is quite long and difficult (much more than replacing the whole upper case). To try if you can find a supplier, have patience and good electro-mechanical skills!