Good thing you found it because the answer is your screwed.
That's actually not true, as long as the the owner has enough hints about the passphrase, it can be brute-forced quite quickly.
And sometimes even keyboard-brute-forced, as proven here.
But beware when people send you their wallet for trying to crack the pass, as it's became a new form of scam, they actually send a trojan instead of a wallet.