The Nature Spirits bound to the Emerald Dream get reborn in the Emerald Dream instead of the World of the Living since they are tethered there by Freya.
Shadra is one of the few Azerothian Nature Spirits not bound to the Emerald Dream as shown by her constant revivals! Nature Spirits leaving the Emerald Dream is a major thing requiring the barriers between worlds weakening like in Cataclysm so Shadra constantly coming back is a sign of her not being bound to the Emerald Dream.
Dreamers(Sleeping Druids, Green Dragons and Cenarius’s offspring) get stuck inside the Emerald Dream upon death. If their kind is not sending their Dreamform into the Emerald Dream when they die(in otherwords like most Druids or Ysera and her mate Eranikus) they go straight to Ardenweald or become Wisps.
The Emerald Dream is between Life and Death in otherwords in the Veil where Players end up when killed thus Spirit Healer Kyrian were able to fetch Ursoc’s Soul and bring it to Ardenweald where he got drained to Permadeath before Shadowlands.