Please post a link to your source on sucralose not breaking down at all in the human body. Please tell us about it.
Not much to tell really. Your body doesn't recognize sucralose and therefore does not obtain any energy from it. That's why it's noncaloric.
Even if your body did metabolize all or some of it, why would you be concerned? Because it contains chlorine? If so, then I suppose you're also afraid of table salt. Given that you're afraid of toothpaste and drinking water, I wouldn't be surprised if salt also scares the heck out of you.