I did a Hefe a few months back as well. I used a starter and it fermented all the way thru and held at the same temp in my garage on the concrete floor so i didn't notice a drop. What i did notice, was tasting when bottling. It was obviously flat but had a very mild spice profile. Bottle that bastard up and give it three weeks before u crack one depending on the ambient temp where u'll be bottle conditioning. Hefe are normally highly carbed and take a little while to get that spice profile to come about. After two weeks I still had a flat hefe with a sub par profile but just after the three week mark the next bottle i popped was perfect.
Either way RDWHAHB, time is very forgiving with brew as im sure u'll come to find out.