Ressurect dead player (that have corpse in instance) before enter to instance.

src: src/game/MapManager.cpp

@@ -217,6 +217,8 @@
                     return false;
                 }
                 sLog.outDebug("MAP: Player '%s' has corpse in instance '%s' and can enter", player->GetName(), mapName);
+                player->ResurrectPlayer(0.5f, false);
+                player->SpawnCorpseBones();
             }
             else
             {

I think this one is already in core