Did you just add straight RO with the liverock? You should have first mixed saltwater, then add the LR to this. The RO probably killed everything that lived on and in the liverock, as they are saltwater organisms. Not much to do about this now, your cycle is going to be long with the die off from the RO.

I would go and explain the predicament to the LFS and ask if you could maybe swap the LR for new pieces, your dead pieces should get seeded with bacteria in their holding tanks in no time. Remember the LR should only be in saltwater.