You don't have to go into total panic mode about this. There is A LOT of pad thickness left after the sensors are exposed. Most people could probably go 5 or 10 thousand miles on them before getting metal to metal contact.
Unless the brake pedal is pulsating when you are applying the brakes, don't even worry about replacing the rotors unless they are very thin. Just replace the pads and make sure you have some new sensors handy when you do it so you can replace the ones that are worn. There are plenty of rotors that are unnecessarily replaced.
As far as the "lip" goes, it will be no problem getting the pads in and out. Make SURE that you remove only one pad at a time. Remove a pad, press that piston all the way back into the bore, put the new pad in place, THEN do the other pad. If you remove both at the same time, the pressure from one piston can push the opposing piston out past the seal which will require disassembling the caliper.
This would be a great time to thoroughly flush the entire brake system and the clutch system if it is a manual transmission.