If it were me I'd replace the caliper which should come with new pads and then I'd scrub the rotor within an inch of it's life.
The primary concern I'd have is that the seal around the piston wasn't seated properly - I'd probably take it apart and try and rebuild it at some point, but that would be something for later. Secondly if the piston has come out then the whole system could need a full drain and rebleed, if there is any water or other contaminants in the fluid that will impact on braking.
The primary concern I'd have is that the seal around the piston wasn't seated properly - I'd probably take it apart and try and rebuild it at some point, but that would be something for later. Secondly if the piston has come out then the whole system could need a full drain and rebleed, if there is any water or other contaminants in the fluid that will impact on braking.