I like AO3 as much as the next fan...
...but it does not currently "archive" fanart (or anything besides text-based fanworks). You can embed and list other fanworks there in an index, but they are *not* preserved.
I want to headdesk every time I see some Tumblr post advising people to back up their "fanworks" to AO3 in the current round of freakouts over Tumblr's corporate overlords and their possible agendas, that pretends as if everything worked like fanfic.
I have fanart on AO3 that will be broken image links if Tumblr goes down, because I embedded some from Tumblr when my own website was particularly glitchy.