Thanks everyone for the advice on the butterfly bushes. I can see where the owners had cut them back two years ago, but not this past fall - the old growth is still there. I'll give them a bit more time to come back, then try planting new ones if they don't. After reading your posts I'm thinking the extra cold winter we just had may have done them in, hopefully it's not because of the spot where they were planted.
Oddly enough, it's the blue/purple shrubs that died off. I also lost two lavendar and two russian sage - they were planted in a different spot.