We know that according to Nozdormu, the Dracthyr were imprisoned 20 Thousand years, but Neltharion only came out as DeathWing 10 Thousand years ago, so, what happened for 10 Thousand years after wielding the power of the void for the first time. Seclusion? Failsafes? Slowly resisting? Did he corrupt his kin all at once or one by one?