What temperatures was it exposed to? Since you really have nothing to lose, smack that sucker and see if it puffs up... Make a starter for the batch and then you should be ok (provided it puffs up first)... The puffing will just be to 'proof' the yeast (show that some are still alive enough to answer the call)...
Yeast love room temps. Now, the downside is that at room temp, all of their biological processes that send them careening towards eventual death occur faster than fridge temps, which is why cold storage is recommended. But you didn't do them any significant damage, so no worries.