I think that is what needs to be worked out by testing.
While the FAA is probably not going to allow any of this, 300' would be too high as helicopters can be in that zone.
If the FAA were to approve it (which they wont), it would have to be at a low height like 50' or less, limited weight, lots of safety features, human observation, not allowed in winds and probably a ton of things I have not thought of.
One could make a foam covered, enclosed fan drone that could do the job that would do little (but not zero) damage if it failed. The problem is that it would still weigh something and could in a failure fall uncontrolled into anything.