If auto takeoff and landing is vital to the mission, you simply have to accept the fact that a GPS glitch during critical phase of flight close to the ground will result in losing your helicopter.
The UAV industry still needs a lot of education.
In the world of full-size aircraft, airports are carefully designed and extensively tested and surveyed for accuracy of radio navigation systems for precision approaches. And those approaches are regularly flown and tested by the civil aviation authority with specially equipped aircraft designed to test and continually certify the approach and radio gear on a recurring basis. The cost is in the millions to meet the requirements and certify an airport for an instrument approach that will use autonomous (slaved autopilot) or radio navigation gear.
https://www.faa.gov/air_traffic/flight_info/aeronav/procedures/ifp_initiation/ifp_requirements/
In the world of UAV’s you are using non-certified, non-TSO’d consumer-grade equipment. Instead of using certiifed and tested ground-based transmitters and gear you are relying on GPS, which is notoriously inaccurate close to the ground. So this is what happens:
If you met all the same requirements as for full size for your takeoff and landing zones, used ground-based navigation systems instead of GPS, and ran a recurring certification process on your systems to make sure they work, it could probably be done quite reliably. But that is not normally the case for UAV’s.