Let's say Nimrod has to roll to break away to do a Running Shot Pulse Wave Nova Blast. Do you announce the RS or PW before the break away roll? If the roll misses, is the NB feat used anyway?

i would say no because you never even made an attack roll. you made a breakaway roll and failed. not a rules judge but thats what i would think.

cheers

Announce you're making a running shot.

Roll for break away.

Move upto half your movement.

Declare your ranged combat action, Pulsewave, for which you'll be using Nova blast.

Roll to hit.

Resolve attack.

Discard Nova Blast.

You have to declare how you're trying to break away - move action, RunShot, whatever - but you don't have to declare what kind of Ranged Combat action you will take until the time to make that attack comes (after the movement). If you fail to make the break away roll, you never get to make the move and hence never get to do your RunShot (so you never have to declare the RC action at all). Failing to break away means you never got to make any attack at all, and therefore you're unable to use NBlast.
If your opponent tried to make it go any other way, he's playing dirty. You don't have to announce what kind of RC Action you're using with RunShot... but even if you actually did tell your opponent the entire plan for what you were doing ("OK, I'll attempt to break away & RunShot, & use a Nova Blast PWave from that square there"), failing the breakaway stops you from going through with any of the further desired steps. That means no movement away, no RunShot activation, no PWave attack, and no use of the feat card. Just because you announced you were going to do it doesn't mean you lose the card.
Perhaps your opponent was confused by the "After resolving this action" stuff at the bottom of the card. The 'this action' the card refers to is the PWave RC action using unmodified dmg value. Since you never got to make said action because you didn't break away, you don't have to discard the card (no matter what you may have announced).