I'm having a hard time believing that. The 2012 Air keyboard is a normal scissor keyboard, there's only the keycap and the scissor plastic thingy beneath it, you can literally repair it with a bit of superglue if you're lucky.
Was it Apple who told you this? Or a 3rd party service center? A reseller? What country did they try to pull this off in?
In 2012, 4-5 days after the purchase of my first and last MacBook Air, they gave me a quote that was half the price of the new MBA when a key cap just popped out. I literally was using it and it popped out.
Their reasoning: physical damage + (this is the kicker) in Air there’s no provision to repair the key or key cap, entire lower board/chassis needs to be replaced.
Yes just a key cap! I shouted to customer support. It was replaced. I decided I am not paying for another fruit company laptop. (In their defence they tried to pull this off in a country with pretty much no or no accessible consumer protection)