You are correct that if you control a Necropotence, you will not lose the game during your draw step, because you will skip your draw step entirely, and you can keep playing until the game ends some other way.
You say "I know if I'm not able to draw on my draw step I lose", but it would be more accurate to say that you lose if you are instructed to draw from an empty library at any time, during your draw step or otherwise.
From the Comprehensive Rules:
120.4. A player who attempts to draw a card from a library with no cards in it loses the game the next time a player would receive priority. (This is a state-based action. See rule 704.)
120.5. If an effect moves cards from a player’s library to that player’s hand without using the word “draw,” the player has not drawn those cards. This makes a difference for abilities that trigger on drawing cards and effects that replace card draws, as well as if the player’s library is empty.