Not quite sure I follow, what is "negative equity"?
It's what this country is swimming in! Kidding. Say you still owe $15,000 on your Hyundai when you decide to turn it in; if they value it at $10,000, it has $5,000 in negative equity. That's under the $7,500 limit, so you owe nothing. The chances of the car depreciating by more than $7,500 in the first 12 months is not likely.