Did you ever play the Frozen Throne Chimp? There are surviving Nerubians as well who were never brought down. You have to fight them as Athas while traveling to the Frozen Throne.
In addition, the Sithilid and Nerubians descended from the same bloodline and eventually split, presumeably on a bad note. This could easily give way to some sort of alliance with alliance forces.
Maybe Dryads could wear two boots and n pants or something
cmon it would be great.