Regular glue or epoxy won't work. It needs to be a conductive epoxy.
The defroster tab fell off of the wife's Liberty last fall. I went to the local Napa and they have a "LOCTITE Defroster Tab Repair Kit." It was easy to use. Be sure you have some isopropyl alcohol or some kind of degreaser to clean the tab and mounting surface.
It has held so far. The defroster is on a lift window, so it gets tugged on every time she opens the back hatch.
I'm sure that O'Reilly's, AutoZone, etc... have kits also.
We had some back glue we used on building carbon fiber arms on our robotic machines at our last job. It held up to a 5G slam and only if the press closed on the arms did they break. I will see if I can get the name and post it for you.