If you heated a chip and it worked for a week, you need to pull the chip, reball the pads & reinstall it. The problem is a bad solder joint (look also for lifted pads). By "the IMEI ic", are you talking about the baseband CPU?
The fundamental cause of losing touch ID when you still have the original home button is that the connector isn't cleanly seated. This is the reason for moving the metal plate underneath the connector and it's also the reason people suggest moving the button over with the heat shield intact, so that you never have to disconnect the home button. In addition, Yes, I often have to do a restore to get the touch ID function back.