As a fellow bostonian I must say that yes, the place will be a zoo, and yes, there are going to be a lot of kegs floating around. But to be on the safe and legal side, the best thing for you to do is wait a month, as kegs in Boston must be returned within 30 days for the return of the $30 deposit. Anyone who misses the deposit cutoff will bring the kegs to the scrapyard and you can get them there instead of stealing them. I got a keg at a scrap yard that had a sticker from 2003 on it, the thing had been sitting in some guys garage for 4 years before he turned it in.
The simplest solution to the problem (for the brewers) as I see it is to set a standard deposit and require liquor stores to pay the deposit to anyone who brings in a keg, regardless of whether the keg comes from the store or not. They require the stores to take back empty cans, so why not for kegs.
I have a Kegerator, and have missed the deposit cutoff before, if it wasn't for the fact that the liquor store was willing to send someone over to collect the keg, it would have sat in my garage for quite a long time, and probably never made it back to the brewery.