Congrats on finishing!
These articles were really great fun, thanks!
As for the Umpani - T´Rang arc, I think that it was clearly unfinished business.
You can always visit Yamir or Z´Ant even right before entering Cosmic Circle and they´re both alive and kicking.
I think that the alliance conclusion is highly satisfying on its own and just assume they were simply late for the party, though I certainly wouldn´t mind, for example, a Rapax Prince megafight with Yamir and Z´Ant on my side.