Well you'll get back some of your HP, but remember, Life Orb takes away HP after you attack, so you won't ever get full HP at the end of a turn with Life Orb + Drain Punch
For example, Breloom has a HP total of 100, but has 50 HP right now. He uses Drain Punch on a Pokémon and gets back exactly 50 HP. However, now, the Life Orb recoil will occur, and Breloom will end up with 90 HP (100 - [10% of 100])
Hope I helped!