Most importantly, don’t overdo it with the spindle. You have correctly noted that the construction is plastic. I would recommend a very small hammer for this. But it can be repaired, it worked for me.
To be clear, the impeller is made from aluminium sheet, sort of riveted together with little tabs extending from the vanes through the plates on its front and back, with what looks a steel bit in the centre which the spindle is pressed through.
The plastic bit is the shroud behind the impeller, which the motor is mounted to.
