Boxing & unboxing is the process of converting a primitive value into an object oriented wrapper class (boxing), or converting a value from an object oriented wrapper class back to the primitive value (unboxing).
The Old Dalaran will stay in Northrend, so yes, mages are going to have 2 portals to dalaran (one to Northrend and one to the Broken Isles)
Peter Lee's 2008 concept of the remnants of Dalaran bordering Alterac Mountains. Dalaran Crater is an area in the Alterac Mountains located at the west end, on the shores of Lordamere Lake. It is north of the Lordamere Internment Camp and just east of Silverpine. It is a massive crater at the original location of the city of Dalaran, which was destroyed during the Third War. The region is still patrolled by Dalaran wizards and their rock elemental minions, who are leveled in their mid thirties. The NPCs around the crater are friendly to the Alliance and hostile to the Horde.