If I were you, I'd make sure this doesn't happen ever, could be expensive. The amount of damage is dependent on the amount of rms power you have and which equipment is turned off or cable unplugged first.
Unplugging preamp, amp and cable while music is playing
I’m wondering what typically happens if you turn off the 1) preamp, 2) the amp, or 3) speaker cable while music is playing, say you accidentally stripped on the power cable of your preamp, amp or the speaker cable and they broke. Does any of these condition will cause any damage to any component for modern equipments?