If you do not install the brake sensor, does the light remain on or would it reset after 2 minutes and never get warned again?

My 2006 E90 330xi has 85k miles, and front-pad never needed to get replaced but my rear pads have been replaced during the warranty (not because the brake pad light came on).

Do you know if BMW's pad squeal when worn down? I have iDrive but the front-pad miles just never seem to go down. I drive a lot of highway miles.

I am wondering if the brake pad sensor is there at all...