If I return a unit with Necromancy to play, from, the discard pile, and said unit dies before the end of the turn, does it:

1) Die and go to the discard pile

2) Die and go to the bottom of my deck

3) Die and go to my discard pile, and at the end of the turn go to the bottom of my deck?

It simply enters your discard pile and stays there. It needs to still be in play at the end of your turn for it to be put at the bottom of your deck.

Which is pretty potent when you use Countess Isara on a Lobber Crew or Snotling Saboteurs. Although the latter is somewhat slower, destruction over and over as needed is pretty strong.