Without looking at it, it's impossible to assess the bolt and/or other hardware that secure the sensor. Ordinarily, one does not have to open the bleed screw when replacing pads unless someone added a bunch when the pads were worn, but if they did, it may need to be bled. I agree with Kazoo, your first call is to the dealer that installed the tires, to allow them to make it right. I'm not certain why they would even need to remove the sensor to install tires, but clearly they did.