After the initial attack (assuming you use speed as the sole determining factor in who gets to strike first), why don't you just have an internal timer that counts down at (1 per tick) * (character's speed rating). This seems to solve all of your problems, if I am understanding them correctly, and is a lot simpler than decrementing stats and having to worry about everyone hitting zero and standing around doing nothing. I can see that you're trying to find an original angle for your battle system, but some things are used frequently simply because they work.
Another possibility is that each time the player or an NPC has a chance to act, you roll that character's speed stat against an enemy's speed stat. Whoever wins that roll gets to act first.
SpaceAce
Another possibility is that each time the player or an NPC has a chance to act, you roll that character's speed stat against an enemy's speed stat. Whoever wins that roll gets to act first.
SpaceAce