Combo points currently do stay on dead things; it's not usually possible to use them, but I often see them when I loot.

I didn't see anything to suggest that you can have combo points on more than one target at a time, which is how it works now. The change just means that you can use non-targeted abilities before generating any more (how long combo points on dead things last is an interesting question, though). Just like today, you can expect putting combo points on a new target to zero any combo points on your previous target.

Redirect is there to reduce the pain of target switching, not eliminate it. Expecting anything more is silly, though I could see an argument for it costing some of the combo points instead of a long cooldown, although if you do that you may as well make it passive.

Which isn't necessarily a bad idea, either; you get a 5-point stack on a target, it dies, and Redirect passively adds half that stack to your new target the first time it's applicable, whether that means your Mutilate crits for a new 5-stack or immediately dropping a 2 point Rupture.