Need Liquid Damage Solution...

my brother in law borrowed my MacBook Air about 2 days ago and ran into a terrible accident with it. "his son vomited on it" he believes no liquid went inside, he tells me that it only got on the screen" but for some reason or another my Mac is not powering On. so i took it to the Apple Store to have it checked out, the Tech took the Lower Cover off and did not find any liquid, he didn't continued taking it apart. he told me that since i told him what happened the Warranty will not cover anything wrong with it i quickly Quoted me on the repairs cost. {my question is what can i do here, can i win this battle with Apple of should i just find someone else to fix it(who and where)?}