I still have the goby in isolation in a Lee's Specimen Container and it is not showing the slightest signs of the disease that killed his 3 tank mates.
Despite this I'm quite hesitant to add it to my main system. It still has another month to go anyway, but this fella is clearly immune to whatever killed the other fish of that shipment - the question is just if he is fully immune (= not a host) or just partially immune (= could spread the disease without being sick).
So I plan to get some "canary" fish, freshwater black mollies that I acclimate to saltwater and put with him.
If they stay healthy he goes in the main system.