Not certain about fish, but in humans and mammals after a week of antibiotics the vast majority of bacterial infections are no longer contagious. (In most cases it's after about 48 hours.)
I'd say that if they're growing new, healthy fins, then the bacteria has been defeated. :)
I had *one* girl in my sorority get fin rot...and she was never QT'd (I thought the others were just nipping at her (and I thought she looked fine otherwise, so let them work it out rather than removing her), it took me about five days to realize she had fin rot...poor thing!), and no-one else came down with it. By the time I realized I just made sure to clean the water really well for a week and she cleared right up.
I know you keep your tanks really clean and well-organized, so your case sounds like it was more stubborn though if it needed antibiotics. But, I still say that if they're growing healthy fins, that I'd assume you're good to go. :)