Well, Adam has said in the past that only a small amount of Hipmunk's traffic comes from Google search results, so they don't really have that far to fall there.
On the other hand, users are fickle and traffic can be a bit butterfly-effecty, so it's hard to predict the impact of something like this. That said, I don't expect Hipmunk to panic or take this lying down.
So who are you rooting for? In the hypothetical world where there is a winner and a loser (which travel search pretty much is, given its maturity), are you rooting for the home team or for the guys you worked with for so long?
On the other hand, users are fickle and traffic can be a bit butterfly-effecty, so it's hard to predict the impact of something like this. That said, I don't expect Hipmunk to panic or take this lying down.