LM5119: Vout when above max duty cycle, i.e., Vin too low?

We have an application where Vin might occasionally drop down close to or below Vout. What happens when Vin drops too low and the max duty cycle spec would need to be exceeded to continue to regulate?

Assume UVLO is set to not trigger due to this lower Vin. If Vin continues to drop, does Vout track it as it falls, with Vout = (Vin) - (DC voltage drops from top FET and inductor) plus a 430nS (max forced HO off time) stopping of current flow every 10uS (100kHz Fsw)?