I find the basic ideas of Sona very appealing, but, from what I see in the web, it is not, by far, as popular as Esperanto or Lojban or other well-known conlangs. Therefore my question: Is it a complete language with a community of fluent speakers, translations of literary works available..? Or is it basically dead?
I think it's pretty much dead.
There is~was a Yahoo group. It has 80 members and no recent activity. But Yahoo groups are all screwed up now, so it's difficult to tell.
There is a dead Sona forum with 14 members. There are a couple translations. No activity since 2010.
There is a dead Sona twitter feed with 13 members. No activity since 2013.
There is a dead Sona tutorial website archived by the Wayback Machine. Not reachable by ordinary means.
The grammar book was hosted online in a now defunct location archived by Wayback Machine.