Do Tapkey-enabled locks have an emergency unlocking mechanism?

The cylinder provides a three-stage battery warning system and you can change the battery from the outside as well. So there is no real way to lock yourself out unless you suffer from vandalism.

For security reasons, there is no built-in functionality to emergency-unlock the Smart Lock. In case of damage, e.g. vandalism, you're options are the same as with a pure mechanical locking cylinder.