I forget the exact words used, but an analogy along the lines of "Going to an abandoned house and placing money in a dresser drawer" was made when I was going over the miner addresses that had been inactive both on Eligius and the blockchain for multiple years.
Aside from the specific matter, it sounds like the lawyer does not grasp how Bitcoin works. Addresses are only ever used by one sender (and normally should only be used for a single transaction), so their activity level is directly related to whether Eligius is sending bitcoins to them. They should never be used for anything else. So
if that was the only factor, I would say they should be assumed to still be active - there is no comparison to an abandoned house, since there is no basis to think they have been abandoned at all.
Just for future reference, or in case anyone else encounters a similar situation...