Yes they could very well be dieing...
Perhaps to shocked when being transported around (nursury-office, office-home). Who knows how long they where sitting neglected...
As for the soil you described, in-organic (rocks and "stuff") soil is actually beneficial to bonsai growth. they do need to be fed (fertilizer, search forum for that), but bonsais don't actually need "earth" to survive.
The following is copied from
this site:
Watering Ensure Junipers are not over watered as they suffer root rot easily, foliage should be misted frequently to help keep pores free of dust enabling them to breathe. In the case of trees that have been recently repotted or have root problems, misting is essential as conifers are able to absorb enough water through their leaf surface to maintain health until the roots are able to support the tree themselves. Misting also avoids excess transpiration and water loss on hot summer days.
More experienced members are bound for chime in and help... Check out the linked site, lots of species specific stuff there...
Merry Christmas, Adam