You will likely need a piston rebuild kit if there is one. You should replace the piston seal and the dust boot. There may be no damage and you could just carefully reassemble it as is but as cheap as these are, you might as well just replace them. You should never apply brakes with no pads/rotor in place unless your intent is to extract the piston (which you’ve done).I have a 2019 Pacifica sport and when I started to retract the brakes in the LCD screen the caliper wouldn’t retract. The screen told me the caliper was retracted and that was not the case. The screen also mentioned to get out of service mode, press the brake and push the parking brake. So I did so and my entire caliper piston shot out with brake fluid everywhere. I’m not a certified mechanic by any means. I Do however learn fast and need some serious help. This is my family’s only means of transport. Is my caliper done? Do I need a new one? I’ll try and post a picture with this. View attachment 50898
And by the way, there normally is no way to retract a brake piston without mechanical persuasion. That would require negative hydraulic pressure (suction). What you have done is to extend the piston beyond its normal operating limits because you disassembled the caliper and left the pads behind. When you applied the brakes there was nothing to keep the piston from simply pushing out of the caliper.