Even if they did take them back to help you "cure" your fish of ich, your water is likely infected with it now and putting them in your tank is going to put them back to square one. If you do a search for "ich" you will find a quadrillion opinions (and experiences) on ich. Everything ranging from, "oh my fish just live with ich, it is fine" to "I saw ich yesterday and today all my fish are dead". Lots of opinions on QT'ing versus not QT'ing.. etc.. etc.. welcome to saltwater !
Anyway, if you truly want to rid yourself of ich, at this point you would probably need to take ALL your fish out and put them into a QT and let your tank run fishless for a period of time to be 100% sure that all the ich parasites are dead before adding any fish back to your display tank. That or help your fish fight ich off themselves by keeping the water healthy, clean and feeding garlic soaked food. If your fish are healthy they can fight off ich themselves, but you will still have ich in your tank. That's my humble opinion
