you can parry him, making him stumble for a bit which will buy you enough time to run far enough.When Hans is in a clawy mood (turns orange, I think. Strikes a Wolverine pose)
YOU. CAN NOT. OUTRUN HIM. Not if he's already close enough that he's trying to leap at you, unless you have a shortcut you can take (like jumping down a ledge) to lose him.
Your best bet is to block him with a melee weapon until he gets bored of clawing and switches to a different mode. Failing that, damaging him enough may convince him to change tactics sooner.
he appears to stop meleeing after he has traveled a certain distance so keep backing up while blocking
with enough medics (and medic nades) a person can full on tank his melee attacks making Hans not use his other attacks, which makes him an easy target until he reaches his next stage (or dies)