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About a week and a half ago I got the "Check brake pads" warning on the digital gauge cluster on my 2020 C43. I was aware that the rear pads were getting a little low, and from what I've read on here it is common for them to be toasted around 20k miles or so (my car is at 21,500). Since the light came on I have driven about 300 miles, and I had a small trip planned next week that would be about 400 miles. How much life is usually left in the pads once this light comes on? I am waiting on new aftermarket rear pads/rotors and they won't arrive in time for my trip. Am I risking any sort of damage to the car/brake failure by waiting this long, and would you guys feel comfortable driving the car in my situation? The front brakes were replaced under warranty about 15k miles ago, and according to my service paperwork about 3k miles ago the fronts are still fine, it's just the rears that are low. Visual inspection says that there is still some pad material left on the outer pad, but I can't see the inner pad at all and don't have the space right now to remove the wheel and check. Any advice is appreciated!
The sensors are hit when there's about 3 MM of brake pad remaining. With "not constantly aggressive" street driving, that means you should have at least 1K mi (probably closer to 2K mi.) of pad remaining. Note that cruise control tends to use the rear brakes for slowing the vehicle and that's often why people wear the rear pads excessively. I normally switch cruise off when going downhill ... can save lots of rear brake pad that way. There's also traction-control "torque braking" wear if you do a lot of aggressive cornering.
WRT damage ... if you burn off the pad material and hit the metal backing pad, you'll still be able to stop just fine (I know this because I once wasn't checking the pads after each track-day session and went completely through the front pads on my C63 S). If you do brake with metal-to-metal, it'll make an apocalyptic grinding noise and you'll score the rotors, but if you're replacing your rotors anyway, that wouldn't be an issue.
BTW, under street-driving conditions, rotors are normally good for at least 2 sets of pads ... often 3 sets. Most (if not all) AMG iron rotors have wear divots that indicate when the rotor is worn down to its replacement thinness. Unless the rotors are showing cracks and/or are scored, you may be able to save the new rotors for the next pad replacement.
Note that the bolts that attach the calipers to the suspension are normally specified as 1-time use. If the sensor was hit, you'll also normally need to replace it with the new pads. You'll also need to move the rear calipers into the maintenance position prior to undoing any bolts. If you search, I think you'll find some good postings and videos on brake maintenance.
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