The only time I've seen them go down in the summer was when they rotted away or dried out completely. If they dried out and the crowns aren't exposed (so they would keep drying) then they would come back. If the opposite happened and it rotted away I'm afraid it isn't likely to return.
Right now mine are sending out a lot of new foliage since it has been raining on and off and has been really cool for August. But I never give them supplemental water at any time of the year in either of the two spots I have them planted - one is on a slope and the other is in sandy soil.
Then again, if you purchased it from a nursery that was watering and fertilizing them like crazy then it could be possible that they couldn't keep themselves going on their own so went dormant. You could probably poke around to see if the crown is still good, and maybe something will come back later.
Good luck with it.