First, use both the throttle failsafe method and also the GCS telemetry heartbeat methods to trigger a failsafe event.
Then for the failsafe event you can configure RTL to fly back to and circle around over a rally point near the origination location.
Include the auto landing sequence as the final waypoints of an automated flight plan.
Then, you can configure RTL to either (a) come back and circle over the rally point, or (b) continue with the mission in which case it will land at the end (provided you have the landing sequence sorted).
I once had the same challenge: I built a do-it-yourself receiver and wanted to make sure the plane came back and landed in case I lost RC control.
You can still have the system perform auto landings without an airspeed sensor. The airspeed sensor gives you more accurate control of the approach airspeeds, but without one the auto-landing feature still works.
I made up an automated mission in Mission Planner. At the end of the mission I entered the commands to perform the auto landing. If I lost RC control then the plane would continue the mission and auto land. If I did not lose RC control I took over and landed the plane manually.