Yes, I agree that you should descend ASAP whenever a manned aircraft is in close proximity. Human lives are more important than losing your $1300 plastic toy.
However if it did crash --- you would NOT be liable in any way. FAA clearly states UAV's may fly up to 400' AGL as long as they are not in restricted airspace. There is not a single court in the United States that could convict you of anything except being a responsible drone pilot.
TOTALLY WRONG.
And...besides the FAR below (which says a helicopter is LEGAL to fly below 400 feet), the helicopter could have been preparing to land in, say, a field, or at a home, or on a road (like if he was Lifeguard)...which are all totally legal. Plus, BOTH "pilots" are responsible to "see and avoid".
READ THIS:
Sec. 91.119 - Minimum safe altitudes: General.
Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:
(a) Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface.
(b) Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft.
(c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.
(d) Helicopters. Helicopters may be operated at less than the minimums prescribed in paragraph(b)or(c)of this section if the operation is conducted without hazard to persons or property on the surface. In addition, each person operating a helicopter shall comply with any routes or altitudes specifically prescribed for helicopters by the Administrator