No way man, there is no overshield. With the Titan and warlock supers it's totally OK to run away in attempt to deny them the points of a kill. I did it earlier today, ran in circles around thieves den and came up behind for the kill. Titan and Warlock can whipe a team if they're all...oh idk... Trying to cap B in control [spoiler] which is hilarious to see btw[/spoiler]. But warlock super has no overshield or insta health regeneration on kill, team shoot and they will die.