There's no inherent risk in prolonged use of headphones provided the volume is kept at reasonable levels (at least according to my otorhinolaryngologist).
Aural isolation is not a problem, on the contrary, the protection from environmental noise provides a rest to the ears that can be beneficial.
Another thing is the tiredness caused by intensive concentration when editing audio, searching for cues, etc. As I understand this is more a mental thing, not a physical one in the hearing aparatus (again, if volumes are kept at confortable level).
Yet another concern is the disconfort caused by using the headphones for long periods of time (skin irritation, hot ears, etc.). If you're planning on many consecutive hours of usage, confort is as much a concern as audio quality (but again, this has nothing to do with loss of hearing risk).