40acre, not sure how good your steth is........?
anyway, with the steth or ear to the hive, you can gently tap the hive, they should be in the top by now. you might have to check/listen from either side or the back. if you hear nothing at all with a tap to the sides of the hive, they are gone.
if you hear them buzz up when you tap the hive, it is possible to put some emergency feed on at 0 celsius (32 f).
have you or can you heft or lift the back of the hive to get a feel for the weight?
like perry said, don't pop the innercover. if your bees are alive, you can place some fondant on top. if you don't have a shim, build one quickly, if need be throw some dry sugar on top the innercover until you can get a shim built to accomodate a fondant or winter patty.
good luck, post back and let us know!