It depends on the forward voltage of D1 in the connection diagram on page 2 of the datasheet. If Vin is higher than the regulating voltage of the converter, and Vin - Vout is higher than D1's forward voltage at the load current, you will get Vin - D1_forward_voltage on the output.
With boost converters, there is always a path from Vin through the inductor and boost diode to the output.