I have decided to use tap fly to get a perfectly straight forward shot while high up. The problem is, there are some areas where the signal completely blanks out in th city I am filming. My question was, if my drone is on a Tap fly mission and it loses signal, will it stop the mission and come back home? Thank you.

Assuming your have RTH enabled it will come back, depending on model it may retrace its steps until its back in signal.

Yes, it will initiate a failsafe RTH providing you have set signal loss to RTH in the app