Someone who really wants to first steal your phone, then go through the following ordeal really needs the information that you protected. Also, still better than a four-digit pin. Of course, we are currently seeing other reasons to not use TouchID as some areas of jurisdictions can force you give up your fingerprint when you are arrested. Here's some advice, don't do anything stupid.
First, the fingerprint of the enroled user is photographed with 2400 dpi resolution. The resulting image is then cleaned up, inverted and laser printed with 1200 dpi onto transparent sheet with a thick toner setting. Finally, pink latex milk or white woodglue is smeared into the pattern created by the toner onto the transparent sheet. After it cures, the thin latex sheet is lifted from the sheet, breathed on to make it a tiny bit moist and then placed onto the sensor to unlock the phone. This process has been used with minor refinements and variations against the vast majority of fingerprint sensors on the market.