Since a fire in a fireplace is an open fire then I would say no that it's NOT safe to leave a fireplace fire burning while gone or asleep.
Sparks could fly out of the fireplace and catch your house on fire.
It's safe to leave an actual wood burning stove going though while you're gone since the flames are contained in the stove and is unable to catch anything else on fire.
If you have a fire going in a fireplace be sure to put the fire out before going to bed or leaving the house.