Observing a motor supplied by a sine voltage, e.g. connected to the mains supply, we can simply assume, that in motoric operation, motor voltage and current have the same direction, resulting in a positive instantaneous power P(t) = V(t)*I(t) > 0, while the signs are opposite in generatoric mode, so P(t) < 0. The motor voltage is mainly representing the rotor emf. More specific, the magnitude represents the rotational speed, and the phase the instantaneous electrical rotor angle. If you change to generator respectively braking, the voltage won't change much, but the current immediately reverses it's sign.
PWM operation is superimposing switch frequent voltages and currents to the above sketched basic motor waveforms. It's average values are however corresponding to the said low frequency waveforms. For a basic PWM model, you don't need to distinguish between transistors and diodes, you can simply assume ideal switches for the equivalent circuit. Furthermore, synchronous switching should be assumed, in other words, in each half bridge, either the high side or low side switch is closed. The duty cycle is representing an average voltage, e.g. 50 % means half of DC bus voltage. This simple model is representing a voltage source, the voltage is set by the PWM generator. By making it smaller or larger than the motor emf, you set the energy flow direction and amount. Generatoric operation generally implies charging the DC bus from the motor. So far a behavioral PWM inverter model, that doesn't care if IGBTs or diodes are carrying the current and how the PWM current waveforms looks like.
To go back to the original problem of IGBT versus transistor current, the current will communitate between both permanently, both in motoric and generatoric operation, but with different duty cycle. In motor operation, the IGBTs will carry the current for more than 50%, so the average DC bus current goes to the motor. In generator operation it's the opposite case.