Where is it mentioned that Gon didn't get his Nen back after being healed by Something/Nanika?
I believe that Gon's aura is still there just not nearly as much as before. i think he gets it back or something because after Gon meets his dad and he and Killua split ways, Gon and his father fight together in the Dark Continent Arch. I'm not sure what happens in that arch yet because I haven't read the manga just yet.