Is it possible to remove the envelope from an LED "filament" bulb and still have it work? Are they in an atmosphere?
There is no special atmosphere inside LED bulbs, some even have ventilation holes. The purpose of the outer envelope is to isolate the user from the mains voltage present on most LED bulbs and to make them mechanically compatible with normal A65 or similar incandescent bulbs.
So, yes it would still work without the envelope but no, you can not remove it due to the electrocution hazard.