For me, a lot depends on whether the stones were actually deliberately toppled (I'm not sure where this Dark Ages date came from in the original post?) or whether they simply fell over because they were badly erected.

If the latter, it doesn't seem right to put them back up because unless you do *another* bad job, you're not really restoring, you're creating a fiction. Whereas we know as a matter of record that the Avebury stones didn't just fall over, but were deliberately toppled. Just a thought.