The FOB I took apart was expendable. I bought it off ebay for $10 because mine was missing the roundel emblem. I never had any intention of making it work with my car. I popped off the emblem and glued it to mine. When I ran across the aforementioned thread, I decided to bust it apart (it had served its purpose) to test some things out.
In retrospect, I don't think I needed to dremmel it. It probably would have popped apart with enough force and an appropriately shaped prybar. It is possible that, assuming your battery is bad, that you could pop it apart and solder a new one (or a good used one) into it and maybe get it working again.
If it's not the battery, the RFID chip may be able to be removed from your board and soldered to a good donor board (from ebay i.e.). I don't know if the RFID chip's ID is used for the locking/unlocking features or if this is burned into one of the other two chips on the board.