If I use sacrifice on a might unit and then save it using Tactical Retreat do I draw 2?

Yes, you do draw 2 cards.

According to RiftJudge FAQ #9425, when you play Sacrifice and use Tactical Retreat to save the unit intended as the sacrifice cost, the following occurs:

1. Playing the Spell: You announce Sacrifice and choose your Mighty unit as the target for the "kill" cost.
2. Paying Costs: You attempt to pay the cost by killing the unit.
3. Replacement: Tactical Retreat's replacement effect intercedes. Instead of the unit going to the trash, it is healed, exhausted, and recalled to your base.
4. Cost Completion: Per Rule 357.2.a, costs that are replaced by replacement effects are still considered paid. Therefore, the cost for Sacrifice is successfully paid.
5. Resolution: Sacrifice resolves, and you draw 2 cards and channel 1 rune.

Your unit survives because the replacement effect of Tactical Retreat changed the outcome of the "kill" instruction (the cost) without preventing the spell from successfully completing its cost payment and resolving its effect.