While I know you're being funny, as a rules question the answer is obvious - if you wait out the surprise round and do nothing, it is just as if you didn't take the surprise round. The surprise round is the time between whenever you start acting and the target's first possible response.
In other words, you can only get a standard action off before the guy is no longer surprised. If you try either a full attack or a CDG, he will be awake and no longer helpless before you are done with either.
If you start raining down the Full Attack, you get off one standard action worth of it before he's aware and moving. If you try to line up a CDG, you wake him up in the process before you do the final thrust.
You want to use that surprise round for something other than the attack. Use it for something that will keep him helpless for the entire next round or two, so that you can get either attack form off.
Plus, honestly, you want more setup for revenge. It is a dish best served cold.

If you let him live until after the quest is over, you have him around to help with the quest. That means you have less chance of dying in the quest, and he'll have even more phat lewt after the quest is done, right?