Gee, Pat-you buy brass chains? No wonder they keep wearing out!!!
FWIW, I doubt anybody has used brass bushings since maybe the victorian era in the way you describe. Brass is very soft and wears quickly. Yes, chain stretch is caused by bearing wear, but I can assure you that those bearings are steel, either annodized or hardened (in any chain worth buying, that is..) not brass. They may be even harder materials. You may find a brass or similar material used in a washer next to a roller, but not on a heavily stressed bearing surface like that.
As far as the chain in question is concerned, yes, it probably became re-tempered. How this has affected the metallurgy depends on the amount of time it was held at what temperature, and how quickly it cooled. Was the chain annodized? If so, then it probably didn't depend on anything like surface hardening for wear reduction. It might be compromised, then again, it might not. Best bet is to get yourself a new chain, and keep this one as a spare, or put it on a beater bike. I'd bet that there's a 50/50 chance it's fine, but odds like that are still hardly encouraging.