Titans can die right as they're activating Fist of Havoc, actually... I've been killed several times attempting it... If They have the "Unstoppable" perk selected then it's nearly impossible to kill them, but you don't get Shoulder Charge... Which I'm guessing most Titans (myself included) would rather run with. Good thing the new Titan exotic helm includes Unstoppable, so now we can have both >:)