There's an indicator in the lower left corner of the discoveries menu that shows if you are currently connected to the servers or not. If I upload my discoveries while it says I'm not connected, will it upload them for other players to see once it gains a connection again?
Based on posts I've read, it sounds like it will save the discoveries you've made and attempt to upload them for real when you do go back online.
And for those who think "But when you explore a world and upload it, what happens in Offline?" well it just waits to be uploaded, until you enter with an online connection again.
However, this could pose an issue if two players discover the same thing while one is offline-- it would appear to be a new discovery to both players, but only one name would be able to be the official name. Other posts suggest that the system would use a first-come first-served basis.
It's who ever uploads it first. So if one in online and one offline the online presone gets it. If both are offline, who ever goes online and uploads first gets it.