The pad that fell off has a rubber substrate so super glue should be fine. Degrease well. Also, if you have a Librands mirror, check that the mounting is not applying pressure to the screen that will hasten the next falling off.
You will now need to carry glue and degreaser on every journey - mine lasted a maximum of 2000 miles between failures once it failed the first time.
I now have an agricultural bracket fixed to the sun visor mounts. It will never fall off. One day, I will get around to tidying it up.
