Are bypass caps reason why uC don't have flyback diode across ferrite bead in the sample schematics?
A typical ferrite bead impedance graph: -



This one peaks around 400 ohms and as you can see the impedance is virtually purely resistive. These are the eddy current losses in the magnetic material. Inductance has dropped off to virtually negligible amounts.

But it does have inductance at low frequencies (and very few losses) so it's worth calculating. At 1 MHz the losses can be assumed zero but the reactance is about 15 ohms (an estimate). So this provides us with the inductance i.e. L = \$X_L/2\pi F\$ = 2.4 uH.

At 20 mA this is inductance holds about 0.48 nJ of energy.

But, given that when you switch your supply off the 20 mA current flowing through the inductor gets benignly absorbed by power supply capacitors on the main power rail I don't think you need to worry.