Is it possible to replace the pads without the sensors? I have not serviced the brakes since I bought the car 1Y ago; and I wonder if the previous owner was diligent.
It is possible to do so; they're very cheap but some do it that way.
ALSO: Depending on the model and features, you may or may not have a sensor at each wheel. My base W210 has them ONLY on the front wheels.
ALSO: If the wear indicator comes on, INSPECT the brakes or plan for imminent replacement. Ignoring or disconnecting the sensor is just asking for a very expensive brake job. If you just replace the sensor (instead of replacing the sensor AND pads) it will wear through and come right back on.
ALSO: Noises should ALWAYS be investigated. Different pad materials can be noisier than others, but don't ignore a noise, and particularly when it's easy to isolate (such as you step on the brake, then you hear it). Pads can wear at slight angles and it's possible to initially get a light scraping sort of sound before you completely ruin the rotors. In any event, don't ignore noises until you have them investigated and know they are safe to ignore.
TO OUR OP: If you have reasonable mechanical skills this is not a difficult job at all, there is a DIY in the diy sticky, check it out. OEM parts are very inexpensive online and the real expense of this job is labor at the shops. F&R pads and sensors for about $90; dealer brake job (without rotors) is about $650. It's a little more work if you also have to do rotors, but still doable if you have basic mechanical skills.
Take care and enjoy the ride,