You can't kill Hans now? I fought him earlier today and kicked his... behind.
Did you just have a berserker face tanking him while being healed by a medic before? The tactics of shooting him seem to work just as well as before.
- Aim for his weak spot
- dive into cover if he starts shooting you
- Don't stand in gas
- Try to avoid his grenades
- Punch him in the face when he starts to melee you while trying to get away but stay near the team if at all possible
- Heal the person he's draining
These are general tips and not steps you do in an order, so it's not a numbered list.