Much of the restoration would be to preserve things as they exist now, and to keep them from decaying further and falling in on tourists.

In the town of Xanten, Germany, there's an "archaeological park" (Archäologischer Park Xanten) at an old Roman fort. Most of what's left are stone columns and foundations that had minimal restoration to keep them from falling apart further, but they rebuilt much of the town as a great educational attraction. It's also my understanding that many of the great stone edifices were, upon the fall of their empires, pillaged for building materials and road paving. The Goths didn't really have historic preservation on their list of priorities.