@M Frary - you are right to be worried, you are in a very cold part of Michigan.
3 days indoors will definitely undo a fair amount of winter hardiness. MSU studies on blueberries & grapes showed that it takes 2 to 3 months of cold below 40 F (+4 C) to acquire full winter hardiness. They used test plants normally hardy to - 15 F (-26 C).
After only 48 hours above 40 F test plants had severe bud damage from a quick change to +5 F (-14 C). This was well inside normal hardiness for varieties tested, yet bud damage was severe.
Take away is that more than a few hours warm in middle of winter can undo winter hardiness.
A recent winter (2011-2012) in Michigan there was a January thaw followed by a spell of "normal" January cold. There was a near total loss of blueberry & grape crops, which prompted the study.