I'm not sure why the tech though you needed a complete logic board replacement as none of your symptoms imply that is the issue here. More often I see damaged trackpads & keyboards or the ribbon connections at either end that have corroded up cause them not to function correctly.
In this series you can access the keyboard & trackpad ribbon cables independently on the logic board. I would start there cleaning them if you see any staining. If after cleaning that doesn't fix things you'll need to move on to the next step here. Be very careful here as these connectors are very fragile! Here is the steps to open them: MacBook Pro 13" Retina Display Mid 2014 Logic Board Replacement. Go though the first six steps disconnecting the battery. Do make sure your system is fully off before you start. Then jump down to Step 27 though Step 30. Using a cotton swab (Q-Tip) dampened with a high grade isopropyl alcohol (85% or better) wipe the ribbon and pins make sure you don't bend the pins of the connector.
Here is where you'll need to think though what is the better direction to just replace the entire uppercase or drill down fixing the trackpad and keyboard. Here is the steps to do this: MacBook Pro 13" Retina Display Mid 2014 Upper Case Replacement While its quite expensive it is a lot less work and gets you going sooner.
Gaining access to trackpad its self is not easy as its under the battery! Here is the needed steps to remove the battery: MacBook Pro 13" Retina Display Mid 2014 Battery Replacement. I should point out once you remove the battery you will need to replace it as you can't reuse it! The force needed to remove it damages it and while it may not look like it, it could start a fire within your system if you try to reuse it. So there is $100 US for the new battery even if it was still working.
Lets move on to the trackpad, I agree its likely damaged here if you couldn't get it working cleaning the ribbon cable. Here is the IFIXIT guide to replace it: MacBook Pro 13" Retina Display Mid 2014 Trackpad Replacement As we have already gone though taking the battery out we can jump down to Step 30 here we are taking the back plate off so we can disconnect the ribbon cable to the trackpad. Here is one place you could have some corrosion from the seepage of what spilled. The trackpads part number is 593-1657 which is about $70
With a new battery connected back in after replacing the trackpad is the keyboard now working? If it is then the battery was damaged by the spill. If not, you'll need to think though your next direction. Replacing the keyboard is a lot of work. You may want to just replace the entire uppercase assembly at that point which is what I would have done at the get go.
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I understand your plight ;-{
But you need to look at this from Apples side for a sec. So what you see here could be just the tip of the iceberg its what is lurking under the water line is what Apple is worried about.
Time and time again many of us have been stung repairing a so called small spill to find it was much more than we had thought. Once they attempt to repair your system they own it until the repair warranty expires and while a quick inspection shows minor damage their maybe more hidden below.
by Dan