To answer one question, it has been my experience that cp stays on a dead target until you put cp on another target or the body disappears on its own. I have killed a mob before finisher, had to vanish to avoid being ganked, sprinted far enough to mount and go to town safely, heal up and come back to loot and see the cp still there.

Backing up, CP is only one one target at a time. If I put 3 points on any target and then switch and SS, the new target has 1 and the old has none.

As such, SnD really doesn't need to know where the CP is since if you have any at all, it's only on one creature, so there is no confusion on the numbers. Dead creatures retain their cp as has been mentioned.
Redirect appears to simply change the property of who has your cp. I imagine if you build up 3 cp and switch and SS before remembering to Redirect, the Rd will likely go on cd and leave you wondering why there is only 1 cp.
Ideally, this means that if something dies, go ahead and SnD as you go to the next target unless you had 5 pts for a redirected finisher. I plan on a macro to put rd with rupture for this since the new mob is fresh and seeing how that works.

Then again, my rogue is only 50, so I may have some misinformation based on limited knowledge.