To say there is no technology would be to say that everything is made of magic, which I am quite sure, it isn't. I can understand things being held together with magic, and with many major thinks being held together with magic, but I do not see absolutely everything having major magical influence. It would:
A) Be a sign of a foolish empire. Anyone who relies too heavily on a few resources will be a fool, since if there were ever an effective counter or blockage, there would be nothing good to repair, build, or continue on with
B) Be foolish in itself, everything being completely unrecoverable. I can see how wreckage from a battle could be non-salvageable, since fighters or turrets could be used to damage it beyond recognition, but there was no one alive.

If any other nation is destroyed, there is salvage. What makes you so special that makes the laws of unspoken rules not apply to you? If the energy source disappears, does the entire city suddenly become nothing but concrete dust?