Bad news is all your accrued vacation days are wiped clean
Why aren't they paid out upon termination? Is that not standard policy in the US? You earnt them, after all. Just as they can't take back your earnt wages, they can't take back your earnt leave.
I don't think it's required by law.
Edit: I guess a fair number of states do have laws for that, though unlimited vacation still gets around that.
The down-side is you get to find out whether they would hire you again if you weren't already on payroll.