I assume you have never touched the trusrod before right ?? Because you brought it to the shop asking to have it checked (because you don't want to do it yourself, because you have no experience with it). The neck was fine (not perfect, but at least not broken) when you gave it to the shop, and it came back like a banana, because the trusrod is busted.........
Indeed, if a tech destroys an instrument and denies responsibility, it is up to the customer (I think) to prove that it actually is the tech's fault...........
I personally would ask what the exact reason is that the entire neck needs to be replaced according to Warwick. If, as Oliver mentioned, it is because some piece of wood was severed by force, then no way you could have done that..........It's a bit complicated for a third person like myself to give advise, because I don't have all the information..............In any case, it's 600$ we're talking about...........I hope you have things sorted out, and please let us know the outcome. Good luck. :wink: