Reset Winding in Single Switch Forward Converter - How To Dissipate Leakage Inductance?
I searched for "single switched forward converter" and read what Wikipedia had to say.   It seems that flyback converters use inductors, which store all their energy in their leakage inductance.  But this circuit uses a transformer, and, "transformers cannot store a significant amount of energy, unlike inductors".  So, your concerns are correct, but apparently the effects of leakage inductance will be far smaller than you are expecting. 

The remark about transformers indicates that almost all of the energy put into the primary is immediately transferred to the secondary and then to the load.